Heat skillet sprayed with cooking spray on medium heat.
Add egg; cook 4 min. or until white is set and yolk is cooked to desired doneness.
Remove from skillet.
Spread bread slices with mayo.
Place 1 bread slice, mayo-side down in skillet; top with ham, egg, Singles and remaining bread slice, mayo-side up. Cook 2 min. on each side or until golden brown on both sides.