If you prefer your bread toasted, begin by toasting the bread. Slice the tomatoes into large rounds (horizontally around the equator of the tomato).
Spread a thick layer of mayonnaise over each slice of bread. Top one slice of bread with tomato slices, then sprinkle a generous pinch of salt and pepper over the tomatoes and second slice of bread.
Close the sandwich with the second slice of bread, cut the sandwich in half, and serve immediately.