Heat oil in a medium saute pan over medium-high heat.  Add jalapeno and onion and saute for 3 minutes, stirring occasionally.  Add the garlic and tomato and continue sauteing for 3 minutes, stirring occasionally.  Season to taste with a pinch of salt and pepper.  Then transfer the mixture to a separate plate.

Return pan to the stove, and reduce heat to medium*.  Add the whisked egg whites and cook for 2-3 minutes until the eggs are set and the bottom of the egg is golden.  Remove from heat.  Add the onion mixture, diced avocado, cilantro and cotija cheese to the egg white, and fold over to form the omelet.  Serve warm, garnished with extra cilantro and cheese if desired.

*Your pan is probably still greased from the olive oil at this point.  But if not, you can add a bit more oil or mist the pan with cooking spray before adding the egg, in order to keep it from sticking.