Line the bottom of an 8-oz. ramekin or custard cup with ham slice, folding ham in half if necessary.
Pour egg over ham.
Sprinkle cheese over egg.
Microwave on HIGH for 30 seconds; stir. Microwave until egg is almost set, 15 to 30 seconds more. Serve immediately.
NOTE: Egg may be added whole, or it may be beaten first, depending on whether you prefer it more scrambled. If egg is too runny in center after 1 minute in the microwave, stir again and cook another 10 or 15 seconds.