Take 4 slices of fresh bread (preferably whole wheat or multigrain).
Apply a thin layer of butter or margarine on one side of each bread slice.
On two of the buttered slices, place a layer of thinly sliced cucumber, tomato, and onion.
Sprinkle a pinch of salt and black pepper over the vegetables.
Place the remaining two buttered slices on top of the vegetable layers, with the buttered side facing down.
Press the sandwiches gently and cut them diagonally into halves or quarters, as per your preference.