My trick, in one word: salsa. Even a jar of supermarket variety salsa perks up egg whites like no other topping. Cheese? Alone it doesn't do the trick. And adding vegetables sometimes seems to make egg whites taste worse, highlighting their lack of flavor. No, adding salsa first is the way to go. Spicy or mango, homemade or store-bought, salsa will rescue your sad egg whites, I promise.
Scramble egg whites as you would traditional eggs, just a bit longer to make sure they are well done. Turn off the heat and top with a few spoonfulls of salsa. For an even better breakfast, add cheddar cheese, crushed tortilla chips, and a few slices of avocado for a simple, egg white version of huevos rancheros. You'll never look at egg whites the same way again!