Heat a little oil in a heavy frying pan/chargrill pan, add the burgers, and use a spatula to press down, to make thin smashed burgers. Cook for 1-2 minutes.
Carefully flip the burgers and cook for a further 1-2 minutes.
Check with a knife to ensure the juices run clear.
Lay the cheese slices on top of the burgers until cheese begins to melt.
While the cheese is melting slice the burger buns in half and lightly toast on the inside.
Spread burger sauce over the base of each bun and layer with salad leaves, tomatoes, gherkins, cheese-topped burgers and more sauce.