Preheat your oven to 350°F (175°C).
In a sizable skillet, brown the ground beef on medium heat until thoroughly cooked. Drain the excess fat.
Add the chopped onion and minced garlic to the skillet with the beef and sauté until the onions are translucent.
Stir in the mixed vegetables, cream of mushroom soup, and milk, and bring the mixture to a simmer. Season with salt and pepper.
Spread the beef mixture evenly in a 9x13 inch baking dish.
Evenly distribute 2 cups of shredded cheddar cheese over the cooked beef.
Neatly layer the tater tots in a single row atop the cheese.
Add an additional 2 cups of cheese on top of the tater tots.
Place in an oven preheated to the necessary temperature and bake for 45 minutes, or until the tater tots turn a crispy golden brown.
Allow the casserole to rest for 5 minutes post-baking to help it firm up before serving.