Preheat oven to 400ºF.
In a medium-size saucepot, heat the leftover gravy over medium-low heat. Once the gravy starts to bubble, mix in the jar of green chili salsa. Remove from heat and reserve.
Spread a thin layer of the gravy/salsa mixture onto the bottom of a casserole dish. Layer 1/3 of the tortillas, 1/3 of the corn, 1/3 of the black beans, 1/3 of the scallions, 1/2 of the meat loaf, 1/3 of the gravy/salsa mixture and 1/3 of the cheese and repeat this process two more times until all of the ingredients are used. Finish with a layer of tortillas, more of the gravy and a final topping of cheese.
Place the "enchil-lasagna" in the oven until the cheese is bubbling and brown, about 10-15 minutes. Top with remaining scallions and serve.