Shape the meat into four burger patties, each weighing 200 g, and press gently in a burger press. Brush the burgers with a little oil, and sprinkle both sides with salt and pepper. Wash the lettuce leaves and tomatoes. Now make the burger dressing. Slice the tomato and remove the seeds. Chop the pickled gherkins finely. Combine the mayonnaise, pickled gherkins and Dijon mustard with a handheld blender. Peel and finely chop the onion and mix with the dressing. Season to taste with salt, pepper and cayenne pepper.
Half fill the Rapidfire® Chimney Starter with Weber® briquettes, light them and prepare the barbecue for direct heat –approx. 240-250°C. Brush the grate with sunflower oil and cook the burgers for around 3-4 minutes on each side. Change the barbecue to indirect heat, move the burgers to indirect and place a slice of cheese on each. Continue cooking until the burgers reach a core temperature of 70°C. Split the buns. Toast on both sides until they have barbecue marks.
Assemble the burger. Spread both halves of the bun with dressing, then place the lettuce leaf, burger patty and cheese, sliced tomato and onion rings on the bottom before putting the top on.