Mix together the onion, breadcrumbs, egg and Worcestershire sauce, then season. Leave for 1 minute for the flavours to absorb, then add the beef mince and combine.
Rub a little oil on your hands and divide the mixture into 4 balls. Roll each ball, gradually flattening it while pressing in the edges so they're even. They should be about 10cm (4in) in diameter and (½ inch) thick.
Place the burgers between 2 sheets of greaseproof paper and put in the fridge for at least 20 minutes to help the mixture bind together.
Grill or fry for 4-5 minutes each side, then serve in baps with lettuce and slices of tomato and red onion.