Preheat oven to 200ºC.
Spread butter on both sides of bread. Arrange on a baking tray and toast in the oven. Turn over and repeat. Remove from oven.
Spread mayonnaise on toast.
Layer chicken, gherkins and lettuce onto 4 slices of toast. Top with another slice of mayonnaise-spread toast. Then top with gammon, lettuce and tomato and the last slices of toast. Slice into triangles, secure with toothpicks or skewers and serve.