Preheat oven to 350°F. Grease a 9x13 inch baking dish with non-stick cooking spray and set aside.
In a large skillet brown the ground beef along with the onion, garlic powder, salt, pepper, and Worcestershire sauce until the beef is no longer pink. Draine grease if necessary.
In a large bowl mix together the beef mixture with the sour cream, soup, green beans, diced tomatoes and 1 cup of the shredded cheese.
Spread the beef and soup mixture into the prepared pan. Top with an even layer of tater tots and bake in the preheated oven for 50 minutes, until tater tots are brown and the casserole is bubbling.
Top the casserole with the remaining shredded cheese and bake for 5 minutes longer until cheese is melted.