Cook the lean ground beef in a large frying pan over medium-high heat until only a little pink remains. Add the onion and garlic and continue to cook for 5 more minutes. Mix the tomatoes and sour cream into the beef then season with salt and pepper.
Pour the creamy beef into a 9x11 inch casserole dish. Top with the corn, then the cheese, then arrange the tater tots in a single layer on the top.
Bake for 25-30 minutes, or until the tater tots are crispy and brown.