Pre-heat oven to 375. Add small amount of olive oil to skillet,
heating on med-high. Add chopped onion and sausage to pan.
When oven is hot, place tortillas directly on oven racks. When
sausage is cooked through, add mushrooms, stirring frequently.
Flip the tortillas to be sure the other side is toasty. When
mushrooms are soft, add egg whites and scramble everything
together. Remove pan from heat.