Preheat oven to 350 degrees F. Have a 13x9-inch baking dish ready. Cook beef and onions in a large nonstick skillet over medium-high heat, breaking up clumps of meat, until meat is no longer pink. Spread meat mixture in baking dish.
Mix soup with milk. Pour soup mixture over top and spread to cover. Sprinkle evenly with cheese, top with tater tots.
Bake 1 hour or until bubbly and tater tots are lightly browned.