Preheat the oven to 375°F, positioning the rack in the top third.

In a skillet over medium heat, cook the bacon pieces until crisp, about 10 minutes. Remove the bacon and place it on a paper towel-lined plate, leaving the rendered fat in the skillet.

Add the ground beef and chopped onion to the skillet. Cook, stirring occasionally and breaking up the meat, until the beef is browned and the onion is softened, approximately 7-8 minutes. Drain most of the excess fat from the skillet.

Mix in the minced garlic and taco seasoning, cooking for about a minute. Turn off the heat, then stir in the condensed soup, sour cream, black beans, corn, diced green chilies, half of the cooked bacon, and 1/2 cup of shredded cheddar cheese. Ensure the mixture is well combined.

Spread the mixture evenly into a 9×13-inch casserole dish. Sprinkle with the remaining cheddar cheese, scatter the reserved bacon, and arrange the tater tots in a single layer over the top.

Bake the casserole uncovered for 45 minutes, or until the tater tots are golden and the cheese is melted and bubbly. If desired, broil for a few minutes at the end, watching closely to prevent burning.

Serve garnished with chopped scallions and adjust seasoning with salt and pepper if needed.