Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.

Bring a large pot of salted water to a boil. Cook the egg noodles for 1 minute less than the package directions for al dente. Drain and set aside.

In a large skillet over medium-high heat, cook the ground beef and diced onion until the beef is browned and the onions are soft. Drain any excess grease.

In a very large mixing bowl, whisk together the tomato soup, cream of mushroom soup, milk, garlic powder, salt, and pepper until smooth.

Add the cooked noodles and the beef mixture to the bowl with the soup mixture. Stir gently until everything is evenly coated.

Pour the mixture into the prepared baking dish and spread it into an even layer. Top evenly with the shredded cheddar cheese.

Bake uncovered for 20 to 25 minutes, until the casserole is bubbly and the cheese is completely melted. Let rest for 5 minutes before serving.