mash the beans with a fork and place in a large bowl. Spray a heavy based frying pan with the oil. Add the onion, garlic and chilli and cook for 3 minutes or until softened. Stir through the cumin. Transfer the onion mixture to the bowl.
Add the zucchini, carrot and the breadcrumbs. Use clean hands to mix the ingredients. Form into 4 balls then flatten to 4 in (10 cm) roungs. Cover and refrigerate for at least 20 minutes.
Heat a heavy-based, non-stick frying pan with the olive oil. Cook the burgers over a medium heat for 2-3 minutes on each side, or until golden and heated through. Spray each side with oil as you cook.
To serve, arrange the salad leaves, beetroot and tomato slices on each bun base. Add a bean burger, some mayonnaise, then place the remaining bun half on top.