Preheat your oven to 350°F (175°C).
In a large skillet over medium heat, add the ground beef, chopped onion, and minced garlic. Cook until the beef is browned and the onions are soft, about 5-7 minutes. Drain excess fat.
Stir in the diced tomatoes (with juice), tomato sauce, Italian seasoning, salt, pepper, and optional frozen peas. Let it simmer for about 10 minutes.
In a large bowl, combine the cooked pasta and milk. Mix well to coat the pasta.
Add the beef mixture to the bowl with the pasta and stir until combined.
Pour the entire mixture into a greased casserole dish. Spread evenly and sprinkle the shredded cheddar cheese on top.
Cover the dish with a baking cover or aluminum foil. Bake in the preheated oven for 30 minutes.
Remove the cover and bake for an additional 15 minutes, or until the cheese is bubbly and golden.
Let the casserole sit for 5 minutes before serving.