Boil the chicken breasts in a pan of water until thoroughly cooked through. Drain and allow to cool.
Meanwhile, remove the crusts and butter the 8 slices of bread. Cut diagonally and place 4 half slices around the outside of the plate, leaving a square gap in the middle. Put a thin layer of torn lettuce leaves into the square gap, sprinkle over some tomatoes, yellow pepper and some cucumber cubes.
Next cut up your cooled, cooked chicken into bite-sized pieces and mix in the mayonnaise, salt and freshly ground black pepper.
Diagonally from one corner of the square to the other, place some chicken and mayonnaise mix. In the two remaining corners place a tomato quarter.
Take 3 pieces of sliced cucumber and cut from the centre to the outside and sit them over the chicken.
Lightly dust the chicken with cayenne pepper and serve immediately.