Cook onions and garlic in 2 tablespoons of cooking oil until they are tender. Remove from heat and stir in pimiento, chilies, and jalapeno peppers cook until tender, and then set aside.
Cook tortillas one at a time, in about 1/4 inch cooking oil in a medium skillet until tortillas are crisp, turning once. Drain on paper towels and set aside.
Melt butter in another saucepan. Stir in flour, chili powder, oregano, salt, and pepper. Add the chicken broth all at once. Cook and stir until thickened and bubbly. Cook and stir for 1 minute more; remove from heat. Stir in sour cream.
Arrange six of the tortillas, overlapping slightly, in an ungreased 3-quart rectangular baking dish. Top with half of the chicken, and half of the cheese. Add a layer of the onion and peppers mixture.
Add another layer of tortillas, the remaining chicken, the remaining cheese, and the remaining peppers. Gently spoon the sauce over the casserole.
Cover loosely with foil. Bake in a 350 degree often for 35 to 40 minutes. Let stand for 10 minutes before cutting. Makes 12 servings.