Mash the garlic, beans, mayonnaise, chilli sauce and lime juice in a large bowl with a potato masher or fork. Stir in the breadcrumbs, spring onions, pepper and a pinch of salt. Shape into 4 patties.
Dredge the patties in the flour, shaking off the excess. Heat the oil in a large nonstick frying pan over moderate heat. Cook the patties for 3 minutes each side or until browned and crisp on the outside and heated through.
Place the patties on hamburger buns and top each with lettuce, tomato and onion.