Grease a 9×13 baking dish with cooking spray and set aside.
Bring a large pot of salted water to a boil. Add the pasta to the pot and cook to just al dente, about 2 minutes less than package instructions. Drain and set aside.
Heat the olive oil in a large nonstick skillet set over medium heat. Add in the diced onion and cook, stirring frequently, until the onion is soft and translucent, about 5 minutes.
Add in the Italian sausage and ground beef, breaking up the meat with a wooden spoon or spatula into smaller pieces.
Cook over medium-high heat for 8 to 10 minutes or until beef and sausage are browned and cooked through. Continue stirring from time to time, breaking up the meat into pieces.
Stir in the minced garlic, Italian seasoning, chili flakes, salt, and pepper. Cook for an additional minute.
Add crushed tomatoes. Stir to combine and simmer for 5 minutes.
Place the cooked pasta in a large bowl. Pour the meat sauce over the pasta and add in the ricotta; mix until well combined.
Place half of the pasta mixture in the prepared baking dish, and spread evenly. Sprinkle with half the shredded mozzarella and half the parmesan cheese. Repeat with a second layer of pasta mixture, mozzarella, and parmesan cheese.
Bake for 30 to 35 minutes or until cheese is golden brown and bubbly at the edges. Remove from the oven and let sit for 10 to 15 minutes before serving.
Garnish with fresh parsley and serve warm.
Notes
Pasta: If you can't find mostaccioli, use any tube-shaped pasta like penne or rigatoni.
Cheese Swaps: Use cottage cheese instead of ricotta and un-smoked provolone as a creamy alternative to mozzarella.
Sauce: Save time by using your favorite store-bought pasta sauce.
Ground Meat: I use a mixture of ground beef and Italian Pork Sausage, but if you prefer to use ground chicken or any other ground meat, go right ahead.
Storing Leftover Mostaccioli: Cover tightly and refrigerate the leftovers for up to 5 days.
Freezing Baked Mostaccioli: You can freeze this baked or unbaked. Wrap it tightly in two layers of plastic wrap and foil and keep it in the freezer for up to 3 months.