Preheat oven to 375 degrees F.
Grease a 9” × 13” baking dish. Reserve 1 cup of the enchilada sauce.
Add the two cans of black beans and 1 can of corn to a colander and rinse. Transfer to a large mixing bowl. Add the green chiles, chopped onion, Rotel, cumin, salt, pepper, and remaining enchilada sauce to the bowl and stir to combine.
Using your hands, remove the chicken meat from the rotisserie chicken, shredding it into small chunks. Add the chicken to the mixing bowl with the other filling ingredients as you shred it. Once all the chicken has been shredded and added to the bowl, stir to combine.
Using a knife, cut the 12 corn tortillas into small squares.
Begin assembling the casserole. Pour a 1/2 cup of the reserved enchilada sauce into the baking dish. Then, using a spoon, spread the sauce to cover the entire bottom of the dish. Next, add a layer of the corn tortilla pieces, then a layer of the filling mixture, followed by a layer of shredded cheese (about 1/3 of the cheese).
From there, add another layer of tortillas, then filling mixture, then another 1/3 of the cheese. Lastly, add another layer of tortilla pieces, followed by the filling mixture, and the remaining shredded cheese. Pour the remaining 1/2 cup of enchilada sauce over the top layer of cheese.
Place the dish into the oven and bake for 20 minutes. Once finished, garnish with the chopped green onions and serve.
