Heat the olive oil in a frying pan and fry the onion over a medium heat for 3 minutes until softened. Add the garlic and chilli powder and fry for a further 2 minutes then tip into a large bowl.
Drain and rinse the beans, add them to the bowl and mash with a fork or potato masher.
Add the breadcrumbs, egg, one quarter of the salsa and half the coriander. Season with salt and pepper and mix it all together.
Divide the burger mix according to the number of people. Wet your hands and shape until burgers. They can now be frozen at this point.
To cook the burgers, place on a non-stick baking tray and grill for 4 - 5 minutes each side until crisp and golden or place on the BBQ 2-3 minutes each side.
Whilst they are cooking, mix the remaining coriander with the yoghurt juice of half the limes and a dash of black pepper.
Cut the burger buns in half and spread each half with a little of the yoghurt mixture.
Add some of the rocket, tomato slices and a spoonful of salsa to the top half of the bun and place the burger in the middle. Serve with the remainder of the salad and the rest of the limes cut into wedges.
In a hurry or not all eating together?These can be prepared in advance and kept in the fridge for 2 - 4 days. Grill when ready.These burgers can be frozen uncooked for up to 3 months. To cook from frozen, pre-heat the oven to 200°C/400°F/gas mark 6. Drizzle both sides with a little olive oil then wrap loosely in foil and bake for 25 - 30 minutes, turning half way through.[nutrition-label]