Pour 1 cup of egg whites into a large skillet, or 1/2 cup at a time if your skillet is small.
Cook egg whites on both sides like a pancake, until no longer runny. Slide egg whites onto a plate. Cut 3-4 inch circles out of the cooked egg whites.
Sautee mushrooms in the hot skillet. Mash avocado in a bowl.
Layer egg white circle, Velveeta cheese, avocado, and mushrooms. Top with more mashed avocado and sprinkle with Everything But the Bagel seasoning and salt as desired.