Spray bottom of slow cooker with non-stick cooking spray.
In a large skillet, cook beef and onion over medium heat until beef is no longer pink. Drain grease, then stir in frozen mixed vegetables, soup, 1/2 cup cheese, milk, sour cream, and seasonings.
Place meat and vegetable mixture in the bottom of the slow cooker. Top with frozen tater tots and shredded cheese.
Cook, covered, on low heat for 6 hours. Let stand, uncovered, 15 minutes before serving.
Notes
We like to serve this with a side salad and warm rolls