Mushroom Meatball Subs with Caramelised Onion Mayonnaise






These meatless mushroom meatball subs are served up in a fresh, homemade spelt subway bun. They also have a slathering of sweet caramelised onion mayonnaise and a dollop of salsa for good measure.

Isn’t it funny how we still call them meatballs even though these contain zero meat? Calling them mushroom balls just wouldn’t sound right. We all know what meatballs taste like. Well, most of us do. And these taste exactly like them. 

I have not eaten meat for three years. It surprises me, sometimes. I never thought I could live without bacon, but I do. For me, it is not about missing meat, but I find it hard to come up with ideas for dinner. Like a good old meatball sub. And when you are hankering for something, you just have to whatever it takes to find a substitute.



Mushrooms as a meat substitute

This recipe for mushroom meatballs is a tried and tested favorite that I often serve with homemade tomato sauce. 

I use mushrooms a lot as a meat substitute. There’s something quite meaty about them, isn’t there? I’ve heard meat eaters scoff at vegetarians wanting to eat something that looks and tastes like meat. Here’s the thing: most of us had eaten meat for a long time. So, a lot of meat dishes are comfort food for us. 

I like to use them in the same way I would use mince, such as bolognese, as seen in my mushroom bolognese garlic bread. If you didn’t know, you would swear you were eating meat. Minced mushrooms, with a few spices thrown in, has the same texture as minced beef. 



Caramelising onions

You don’t need to caramelise the onions for the mayonnaise. Doing it properly takes time, something we don’t always have. However, if you want to make the most delicious mayonnaise ever to exist, you should. Seriously though, caramelising onions elevates the flavour and well worth taking the time to do it. 

If you’ve never made caramelised onions before, don’t let the name fool you. There’s no sugar added. Onions are naturally sweet when cooked. If you add a touch of butter and/or olive oil and give them at least 20 minutes, the sweetness (and flavour) intensifies. 



Spelt subway bread

The last part of the dish is the bread. Some might say the most important part. 

As with the caramelised onions, you don’t need to make your own bread. Just find a soft sub roll, and you’re good to go. However, if you would like to switch up the sandwich to another level, make your own spelt subway buns.

I make my own bread buns using just spelt flour, and they are amazing. Check out my super soft spelt buns and spelt hot dog buns. Yes, spelt can be a little finicky (it behaves a little differently to regular flour). However, once you get the hang of making it, you will never eat normal bread again. 



If you like this recipe for mushroom meatball subs, check out my other savoury dishes.


Mushroom Meatball Subs with Caramelised Onion Mayonnaise


Subway Rolls (see recipe here)

    Mushroom Meatballs:

    • 1 tablespoon olive oil
    • 1 tablespoon butter
    • 1 small red onion (finely chopped) see note 1
    • 250g (9 oz) mushrooms (finely chopped) see note 2
    • 1 teaspoon minced garlic
    • 1 tablespoon Worcestershire sauce
    • 1 teaspoon salt
    • 1 teaspoon black pepper
    • 1 teaspoon paprika
    • 1 teaspoon oregano
    • 50g (1 cup) breadcrumbs
    • 50g (1¾ oz) mozzarella (grated)
    • 1 egg beaten

    Caramelised Onion Mayonnaise:

    • 1 tbsp olive oil
    • 2 tbsp butter
    • 2 large yellow onions
    • 1 tbsp Worcestershire sauce
    • mayonnaise

    Additional Ingredients:

    • salad accompaniments
    • salsa (optional)
    • mozzarella (optional)


    Caramelised Onion Mayonnaise:

    • Add the olive oil and butter to a pan and heat together.
    • Thickly slice the onions and add to the butter and oil.
    • Let them cook for five minutes, then add the Worcester sauce.
    • Continue to cool them on medium heat for around 20-30 minutes, stirring occasionally to make sure they aren't sticking. If they are cooking too quickly (starting to burn), turn the heat down.
    • When ready, spoon into a bowl, and allow them to cool completely.
    • When cooled, stir in as much mayonnaise as you like (I used around 1 cup / 250ml).

    Mushroom Meatballs:

    • Add the olive oil and butter to a pan.
    • When ready, add the chopped onions, and fry until soft.
    • Add the mushrooms, garlic, Worcester sauce, seasoning and spices. Stir until combined and cook for around five minutes.
    • Remove from the heat and allow to cool.
    • When ready, beat an egg in a large bowl.
    • Add the breadcrumbs and mushroom mixture, and give it a good stir to make sure it's well combined.
    • Using your hands, roll into balls, and place on a dish lined with baking paper.
    • Pop the mushroom meatballs in the freezer for 30 minutes to firm up.
    • When ready, fry in a little oil, or cook in your Airfryer (which is what I did). Handle them carefully, as they can be a little fragile.


    • Slice the subway buns in half.
    • Apply a very thick spread of onion mayonnaise to one (or both) halves of the bread.
    • Use any kind of salad you want, and add it to one half of the bread. Top with the meatballs, along with a sprinkling of mozzarella and salsa (if using). Enjoy!


    1. You can use either yellow/brown or red onions.
    2. I blitzed my mushrooms in a food processor as they feel more like "minced meat".
    I have converted grams to cups/ounces/tablespoons using online converters. Although I have no reason to believe they are inaccurate, please be aware that I have not made the recipe with imperial measurements.
    In addition, many ingredients are different in Europe compared to North America. I do all I can to offer possible alternatives and to ensure the best possible outcomes for everyone. However, results cannot always be guaranteed if you have not used the same ingredients, measurements or methods as me.
    Lastly, I do everything I can to ensure that my recipes (and instructions) are accurate and easy to follow. However, I am human, and don't always get it right. If you notice anything strange, a mistake, or even a typo, please let me know in the comments. 



    Mushroom Meatball Subs with Caramelised Onion MayonnaiseMushroom Meatball Subs with Caramelised Onion MayonnaiseMushroom Meatball Subs with Caramelised Onion MayonnaiseMushroom Meatball Subs with Caramelised Onion Mayonnaise

    Do you have a question or comment? I'd love to hear from you!