Preheat the oven to 350 degrees F. Spray a 9×13-inch baking dish with non-stick spray. Set aside.
Cook and crumble the ground beef with the diced onion in a large skillet. Cook over medium heat until the beef is no longer pink. Drain any grease. Add the minced garlic; cook and stir for 1 minute. Add taco seasoning and water. Stir until well combined. Stir in the salsa, green chilies, and black beans. Reduce heat to low and continue to stir until fully heated through.
Line the bottom of the prepared baking dish with 6 corn tortillas, slightly overlapping to cover the bottom of the dish. Spread 1⁄3 of the meat mixture evenly over the tortillas. Sprinkle 1 ½ cups of cheese evenly over the meat mixture.
Continue layering the corn tortillas, beef mixture, and cheese to form three layers total. Ending with the cheese on top.
Cover dish with foil and bake for 30 to 40 minutes until the cheese is melted and bubbly. Carefully remove from the oven and remove foil. Garnish the top with the diced tomatoes and green onion. Allow lasagna to stand for at least 5 minutes before slicing and serving. Enjoy!