Preheat your oven to 350°F (175°C).
In a large skillet, brown the ground beef over medium heat until fully cooked, about 7-10 minutes. Drain any excess fat.
Add the chopped onion and minced garlic to the skillet with the beef. Cook until softened, about 5 minutes.
Stir in the diced tomatoes, tomato sauce, oregano, basil, salt, and pepper. Simmer for 5 minutes.
Meanwhile, cook the gluten-free pasta according to package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine the cooked pasta, meat mixture, and milk. Mix well.
Pour the mixture into the prepared 9x13-inch casserole dish. Top with shredded mozzarella and cheddar cheeses.
Bake in the preheated oven for 20 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let it cool for 5 minutes before serving.