Preheat the oven to 375°F (190°C).
In a large skillet over medium heat, brown the ground beef along with the diced onion until the meat is cooked through and the onion is translucent, around 5 to 7 minutes. Drain any excess fat.
Stir in the cream of mushroom soup, cream of chicken soup, frozen mixed vegetables, garlic powder, Worcestershire sauce, salt, and pepper. Mix until well combined and heated through, about 3-5 minutes.
Pour the beef mixture into the bottom of a greased 9x13-inch baking dish, spreading it out evenly.
Arrange the tater tots in a single layer on top of the beef mixture.
Bake in the preheated oven for 25 minutes.
After 25 minutes, remove the casserole from the oven and sprinkle shredded cheddar cheese evenly on top. Return to the oven and bake for an additional 10-15 minutes, or until the cheese is melted and the tater tots are golden brown.
Once done, take the casserole out of the oven and let it sit for a few minutes before serving.