Preheat oven to 400°F
Spread the tater tots out in a single layer on a large baking sheet and bake at 400F for 15 minutes
While the tater tots are baking, heat the olive oil in a large skillet over medium heat. Add the onions and sauté until softened, about 3-4 minutes
Crumble the ground beef into the skillet and sauté, stirring often, until completely browned
Add garlic and quickly stir to cook, don't let it brown or burn
Drain off excess fat as needed, add the taco seasoning and water to the meat and stir well
Simmer over medium heat for 1-2 minutes, then remove from the heat
In a large mixing bowl, combine the ground beef mixture, black beans, corn, green chiles, enchilada sauce and 2 cups of the shredded cheese and stir well
Grease a 9x13 inch glass baking dish with non-stick cooking spray
Pour the enchilada filling mixture into the dish
Take the tots out of the oven and arrange the tater tots over the top in a single layer
Top the casserole with the remaining 1 cup of shredded cheese
Reduce the oven heat to 375°F
Bake the casserole uncovered for 30 minutes or until the cheese is melted and the casserole is bubbling around the edges
Cool the casserole slightly, then serve with the toppings of your choice.