Pre heat your oven to 350 degrees and bring a large pot of water to a boil.
Heat the olive oil in a large pan over medium heat. Add half of the meatballs, breaking them apart with a wooden spoon. Brown the meatballs and continue breaking them up into crumbles. Add the onion, garlic and rosemary, stir and cook until the onions have started to soften; about 5 minutes. Stir in the tomato paste and cook for an additional 2 minutes. Add the tomatoes along with the tomato sauce. Add the salt, oregano and red pepper flakes. Lower the heat to medium low and simmer the sauce for 5-10 minutes.
Salt the boiling water and add the pasta. Cook the pasta to 2 minutes less than package directions for al dente. Reserve 1 cup of pasta water and drain.
Add a bit of the sauce and a splash of reserved pasta water to the bottom of a 9x13 baking dish. Layer half the pasta, followed half of the sauce and half of the ricotta. Give it a stir to make sure each piece of piece of pasta has some sauce on it, but leave some of the ricotta in chunks for texture. Layer half of the mozzarella on top. Repeat these steps with the second half of the ingredients. Cut the remaining meatballs in half and arrange them on top of the pasta.
Loosely cover the baking dish with foil and bake for 25 minutes then broil for 10 minutes uncovered or until the cheese is bubbly, the meatballs are browned on top, and the edges are crispy.
Let the pasta rest for about 10 minutes before cutting into it. Garnish with fresh parsley and Pecorino Romano and serve!