With a touch of olive oil, smother mustard greens and onions in a hot skillet until mustard is wilted. Spoon out of pan and set aside. Whisk together egg whites, salt & pepper, and Tabasco. Poor mixture into skillet and cook on medium heat until the omelet begins to cook in the middle. Spoon smothered mustard and onions (along with remaining ingredients) evenly onto 1/2 of the omelet and fold. Reduce heat and continue to flip until brown.