Spray a 9x13 inch baking dish with gluten-free nonstick cooking spray and preheat the oven to 375 degrees.
Heat oil in a large skillet over medium-high heat and sauté onion until translucent, about 5 minutes. Add the garlic and cook, stirring, for 30 seconds. Add the ground chicken and cook, breaking it up with a spatula and stirring occasionally for about 5 minutes. Add taco seasoning, green chilies, enchilada sauce, black beans, and corn. Sauté for about 5 minutes, stirring occasionally.
Add about 1½ cups shredded cheese and stir well to combine.
If your skillet is not large enough to hold everything, transfer to a large mixing bowl and stir well.
Scoop the mixture into the prepared baking dish. Top with tater tots and sprinkle on the remaining shredded Mexican blend cheese and the cotija cheese. Bake for about 25-30 minutes or until hot and bubbly and the tater tots are crispy.
Top with diced tomato, sliced black olives, jalapenos, sour cream, cilantro, or other taco toppings of choice.