This is something I make pretty often; especially on the weekends when I'm hungover or on a time crunch because it's pretty damn easy to put together and fills me up. I make it with egg whites, American cheese (sometimes feta if I'm feeling fancy, but I'll admit I like American), tomatoes, lettuce and hot sauce on whole wheat toast. Nums..
Toast the bread lightly and put aside. Put lettuce on one side of the bread, cut the tomato into round slices and place on top of the lettuce.
Pour the egg whites into a hot, lightly greased pan (I use cooking spray usually), stir around in a circular motion with a fork a few times until they start to come together and almost look scrambled. Cook for 1-2 minutes. This is my method for making omelettes, by the way. But if you have a preferred method, go right ahead and do that. Flip the eggs so the other side cooks for about a minute. Put the cheese slice in the middle and fold over. Cut in half and stack on top of one another on the other piece of bread.
Drizzle with the hot sauce and put sandwich together.
Take a bite.
Note: there will most likely be tomato/hot sauce dribble running down your fingers when you bite into it.