Preheat oven to 375F (use convection if you have it) and spray a 10-inch oven-proof skillet with cooking spray.
To the bottom of the skillet, add 4 to 5 tostadas, enough to completely cover the base of the skillet, breaking them slightly if necessary to get complete coverage (does not have to be perfect).
Evenly top with one-third of the salsa (8 ounces), one third of the chicken (1 cup), and one-third of the cheese (4 ounces).
Repeat the layering process twice. Tostadas, salsa, chicken, cheese.
Bake for about 25 to 30 minutes, or until the cheese is as lightly golden browned as desired.
Optionally garnish with cilantro, tomatoes, or your favorite garnishes (read blog post for ideas). Serve immediately. Chilaquiles are best fresh.
