Arrange 6 tortillas on a parchment-lined baking sheet.
Pour a small amount of sauce over each, then sprinkle with the optional minced onion. Top with half of the grated cheese. Top with another tortilla and repeat the layers.
Place the plates in the oven for 10 minutes, or just until the cheese melts.
Allow the plates to cool a bit, then garnish with shredded lettuce and black olives.