1. Take a large frying pan and place it over a medium heat. Add in a splash of oil. When the oil is hot, toss in the onion, red pepper and garlic along with a pinch of salt and the chopped red chillies if using. Stir-fry for roughly three minutes then tip into a bowl and allow to cool.
2. Drain the black beans in a colander and rinse with cold water until it runs clear. Line a tray with a tea towel and tip the beans into the tray, patting the top dry with another tea towel to remove as much water as possible. Place half of the beans into a large bowl and mash well with a fork.
3. Cut the softened sweet potato in half before scooping out the flesh and adding to the bowl along with the remaining black beans. Add in the onion and pepper mix, sweetcorn, breadcrumbs, paprika and watercress and use your hands to combine everything thoroughly. Season the mix to taste with salt and pepper.
4. Form four large patties and leave to chill in the fridge for at least half an hour before cooking.
5. Pre-heat the oven to 180°C. Wipe out the frying pan you used for the onion and pepper mix and return to a medium heat. Add a splash of oil into the pan. Once the oil is hot use a spatula or slice to carefully place each burger patty into the pan. Fry for 2-3 minutes on each side before placing into the oven for 10 minutes or until piping hot throughout.
6. Remove the patties from the oven and leave to rest for a minute while you prepare the buns. Slice the buns in half and toast (either under the grill or in the toaster). Slice the avocado. Place a burger on the bottom of each bun, then top with avocado slices and a good dollop of tomato relish or other sauce. Serve and enjoy! You could also top the burgers with a variety of other fillings including sliced tomatoes, fresh watercress or sliced red onions.
Our thanks to www.watercress.co.uk for providing this recipe
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