These are the best of taco night and pizza night rolled into one! Slideshow: More Mexican Recipes
In a large heavy skillet, heat the oil over medium high heat until hot, then stir in the on-ion, garlic, 1/2 teaspoon salt and 1/4 teaspoon pepper and cook, stirring occasionally, until golden, about 6 minutes. Stir in the tomatoes with their juices, oregano, and chick-en, and cook until the chicken is cooked and the liquid is slightly thickened, about 10 minutes. Season the filling with salt and pepper to taste. Reserve 1/2 cup of the tomato sauce.
Preheat the oven to 350°F. Divide the filling between the tortillas. Roll each tortilla into a cylinder and place, side-by-side in a baking dish. Pour the reserved tomato sauce over the tortillas, sprinkle with the cheese and place the pepperoni over the enchiladas.
Bake the enchiladas until the filling is hot and the cheese is melted, about 10 minutes. Serve.