Preheat oven to 375 °F.
Lay tortillas directly on oven rack and bake until starting to puff up, and become crispy, about 4 minutes. Carefully remove tortillas from oven and place on baking sheets. Evenly sprinkle tortillas with grated cheese; bake until cheese is melted and almost bubbling, about 3 minutes more.
Remove tortillas from oven; transfer to plates. Evenly divide remaining ingredients among tortillas; serve immediately. Enjoy tostadas whole or slice into pieces almost like a Mexican-style pizza.