Tip the beans into a large bowl, then roughly crush with a potato masher. Add in the breadcrumbs, paprika powder, coriander stalks and ½ the chopped leaves, egg and 2 tablespoons tomato salsa, season to taste and mix together well with a fork. Divide the mixture into 4. To form into burgers, wet your hands and shape into burgers. To cook, either fry in a pan with a little olive oil for 10 minutes, or alternatively place on a non-stick baking tray and drizzle with olive oil. Bake in the oven at 200`c for 10-15 minutes. While the burgers are cooking, mix the remaining coriander leaves with the yogurt, lime juice and a good grind of black pepper. Split the buns in half and spread the bases with some of the yogurt. Top each with leaves, a burger, avocado and onion slices, another dollop of the lime yogurt and some salsa. Place on the top of the bun and serve.