Preheat your oven to 180°C/160°C Fan/Gas 4
Drain, rinse and dry the black beans with kitchen roll or a tea towel. Spread in an even layer on an oven tray lined with foil. Cook for 8 minutes and then add the chopped brazil nuts on top and bake for a further 8 minutes. You are looking for the beans to appear dry and cracked and the nuts to be lightly browned. Once cooked, set aside to cool.
Heat a tablespoon of olive oil in a pan and fry the sweet potatoes on each side until they are soft and browned (about 2 mins on each side) Once cooked remove and set aside.
Using the same pan add the mushrooms with a sprinkling of sea salt and cook for around 4 mins until they're browned.
In a food processor add the cooled beans and nuts and pulse for around 30 seconds until they resemble breadcrumbs - a bit of texture is fine.
Add the sweet potatoes, mushrooms, sea salt, cumin and chilli powder and pulse for a further 30 seconds until combined. Again, texture is good - you don't want a gloopy mess!
Tip all the ingredients into a large bowl and stirl through the quinoa and BBQ sauce. Add more quinoa if the mixture is too wet or a little water if it's too dry. Taste and adjust seasoning.
Divide the mixture into 4 equal parts and use your hands to press the mixture into patties. Pop them on a plate, cover with cling film and leave them in the fridge for 30 minutes to firm up.
When you're ready to cook the burgers you can griddle them on both sides for a couple of minutes or until they are golden brown. Finish them in the oven 180°C/160°C Fan/Gas 4 for 12 minutes so that they are cooked and hot all the way through. Once cooked you could then put them on the BBQ for a more authentic BBQ experience but this is totally optional!
Assemble the burgers by slicing a bun in half, adding lettuce, then the burger patty top with whatever you fancy. I used cheese, pickles, tomato, red cabbage and onion rings and added an extra dollop of BBQ sauce.