Using a biscuit cutter or round cookie cutter, cut out center of 1 slice of bread (discard center or save for another use). Spread mayonnaise on 1 side of bread slices. In a large skillet coated with cooking spray, lightly toast cutout slice, mayonnaise side down, over medium-low heat. Flip slice; crack an egg into center. Add remaining bread slice mayonnaise side down, to skillet; layer with cheese and bacon. , Cook, covered, until egg white is set, yolk is soft-set and cheese begins to melt. If needed, flip slice with egg to finish cooking. To assemble sandwich, use solid slice as bottom and cutout slice as top.