Preheat oven to 400 degrees F. Spray a 9 inch cake pan with non stick cooking spray.
In a large skillet heat oil over medium high heat. Cook tortillas 1-2 minutes on each side or until crisp.
Lay one tortilla on the bottom of your prepared cake pan. Spread with 2-3 tablespoons of sour cream. Top with chicken and cheese.
Repeat this process 3 more times. Top the last tortilla with the remaining amount of cheese.
Bake for 25-30 minutes or until heated through.
Top with tomato and avocado if desired. Serve with sour cream and salsa if desired.