Mix 500g of lean beef mince with 1 tsp chilli powder and season. divide the mixture into 4 equal pieces, then shape with your hands into round burgers about the width of the buns. Grill on the barbecue for 5 minutes on each side, or until cooked through.
Meanwhile, toast 4 burger baps on the barbecue. Serve with tomatoes, gherkin and chopped onion.