Crack the egg into a microwave-safe cereal bowl and whisk in the milk. Season with salt and pepper. Cook in the microwave on 100% power for 1 to 2 minutes, or until cooked through.
While the egg is cooking, toast the bread. Use a spoon to remove the cooked egg from the bowl and set it on one piece of toast. Top with a slice of cheese and the other piece of toast. Cook in the microwave until cheese is melted, about 15 seconds.