Pre-heat the oven to 350. Lightly mist a 9×13 baking dish with cooking spray. Drizzle about 1/3 cup of the enchilada sauce across the bottom of the dish and spread around with the back of a spoon to lightly coat the bottom of the dish. Arrange 4 ½ of the tortillas across the bottom of the dish to cover the majority of the space (my arrangement is pictured above). Use a spatula to spread the refried beans evenly across the tortillas, forming an even layer across the whole dish. Set aside.

In a large skillet or saute pan, bring the oil to medium heat. Add the chopped chicken and diced onion and stir to coat in the oil. Cook, stirring occasionally, until the chicken is cooked through and the onions are softened (6-10 minutes). Drain the liquid from the pan if necessary. Add all the remaining enchilada sauce, the black beans and the corn and stir together. Remove from heat.

Spoon about half of the chicken and sauce mixture evenly across the top of the refried bean layer in the casserole dish. Sprinkle about half of the cheddar cheese evenly across as well. Arrange the remaining 4 ½ tortillas in a similar style to step 1 (I did the same but flipped the layout so any small missing spots from layer 1 would be covered and vice versa). Spoon the remaining chicken and sauce mixture evenly across the newly laid tortillas. Sprinkle the remaining cheese over the top. Bake in the oven for 30 minutes. Cut into 8 pieces and serve.