Preheat the oven to 400°F
Place corn tortillas on a baking sheet
Brush or spray both sides lightly with oil
Bake for 5 to 8 minutes
Flip tortillas halfway through baking
Remove when golden and crisp
Heat refried beans if using
Spread beans on each tostada shell
Add cooked meat, chicken, or seafood if desired
Top with lettuce, tomatoes, cheese, avocado, salsa, and sour cream
Serve immediately