Preheat oven to 450°F (232°C). Line a large baking sheet with foil for easy cleanup.
Bake tortillas: Lightly brush both sides of the corn tortillas with oil and arrange them snugly on the baking sheet. Bake for 9 to 10 minutes, until the tortillas are firm but not browned. Let cool for about 5 minutes.
Flip and layer: Flip tortillas over and spread each with refried beans. Add shredded rotisserie chicken and top with shredded cheese.
Return to oven: Bake again for 5 to 6 minutes, until the cheese is melted and everything is heated through.
Add toppings: Garnish each tostada with your choice of sour cream, red onion, cilantro, tomatoes, hot sauce, and any other favorite toppings. Serve immediately.