1Put the meat and Worcestershire sauce in a bowl and season with black pepper and 1 generous tsp salt. Mix together well, then shape the meat into 4 thin, flat burgers. Chill until needed. Can be made a day ahead. Combine the chipotle paste, ketchup and mayonnaise in a bowl to make a sauce.
2Heat a gas or charcoal barbecue to high (or you can use a griddle pan on the hob). Cook the burgers over direct heat for 2 mins each side or until grill marks appear. Top each with 2 slices of cheese and cook for another 30 secs or until melted, then remove from the heat. Toast the buns for a few seconds on the cut-side.
3Spread a little of the spicy sauce on the base of each bun and top with lettuce, tomato, a burger patty, onion and pickles. Top with the bun lid and devour immediately.