Make a ‘flax egg’ by mixing the flaxseed and water together and leaving aside to form a gel.
Pour a splash of olive oil into a large frying pan and bring to a medium heat.
Add the onion and sauté until soft.
Add the mushrooms and cook for about two minutes.
Mix the garlic in and stir for another half a minute, until fragrant but not browning.
Remove the onions, garlic and mushrooms from the heat and tip them into a large mixing bowl.
Add the black beans and mash to desired consistency.
Add the cooked quinoa, cooked beetroot and all the herbs and spices. Season well.
Mix all ingredients together until they’re thoroughly combined. If it feels too loose, add the ‘flax egg’ to bind it together better. If you prefer a chunky burger, mix by hand, and if you prefer a smoother taste, use a food processor.
Using your hands, form 1-inch-thick circular patties from the mixture and pop into the fridge to set for half an hour.
Pre-heat the oven to 180°C / gas mark 4.
Pour the remaining olive oil into an oven-proof pan and bring to a medium heat.
Cook the patties for about three minutes on each side until crispy and then pop the pan in the oven for a further five minutes to ensure they’re piping hot throughout.
Serve with accompaniments of your choice, such as burger buns, vegan cheese and fresh salad.