Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch (23x33 cm) baking dish with non-stick cooking spray. (For extra crispy tater tots, place the frozen tots on a separate baking sheet and pre-bake them for 10 minutes while you prepare the meat).
In a large skillet over medium-high heat, cook the ground beef and diced onion together until the meat is completely browned and no pink remains. Add the minced garlic and cook for 1 additional minute until fragrant. Carefully drain any excess grease from the skillet using a colander.
Reduce the heat to medium. Stir the diced green chiles, taco seasoning mix, drained black beans, and frozen corn directly into the beef. Mix well to combine. Remove the skillet from the heat entirely and gently fold in 2 cups (approx: 225g) of the shredded Mexican cheese until completely melted and sticky.
Pour the cheesy beef mixture into your prepared 9x13 baking dish. Use a spatula to press it down into a smooth, even, tightly packed layer. Arrange the frozen tater tots in a tight, single layer, completely covering the meat mixture so no beef is exposed.
Drizzle the red enchilada sauce as slowly and evenly as possible over the entire layer of tater tots. Place the uncovered baking dish on the center rack of your oven and bake for 30 to 40 minutes, or until the sauce is actively bubbling around the edges and the tater tots are deeply toasted and crispy.
Remove the hot dish from the oven and sprinkle the remaining 1 cup (approx: 115g) of shredded cheese evenly over the top of the crispy potatoes. Return the casserole to the oven for just 2 to 3 minutes, until the cheese is beautifully melted. Let the dish rest on the counter for 5 minutes before topping with fresh cilantro, sour cream, sliced olives, and diced tomatoes. Serve hot!