Heat a 10-inch, non-stick skillet greased with olive oil over high heat. Toast tortilla on both sides until there are golden brown marks and it becomes slightly crispy.
Remove to a plate and immediately sprinkle with the cheese.
Add enough olive oil to prevent egg from sticking and pour the egg mixture into the pan. Swirl gently so that the egg mixture covers the bottom of the pan evenly and cook as you would an omelet. It will cook quickly as it is thin. Sometimes, I cook until golden brown on the bottom and almost cooked through without flipping. That way, there is a crusty bottom with just a touch of moisture on the top. Top with a pinch of salt and pepper.
When cooked to your liking, remove the egg from the pan as one big circle and place on top of the cheese-covered tortilla. Fold in half (or roll) and and top with salsa, if desired.