Boil pasta in salted water until al dente, drain and set aside.

Heat olive oil in large skillet, add sausage and onion. Cook over medium-high heat, stirring to crumble the sausage. Once browned, add garlic and heat for a few minutes. Add the marinara and red pepper flakes. Stir to incorporate all ingredients and bring sauce to a low boil.  Stir in the drained pasta, mozzarella and ¾ cup of the Parmesan cheese. Cover and let the combination heat through for a few minutes. Remove skillet from heat, uncover pan and top with dollops of ricotta cheese and the rest of the Parmesan cheese. Serve immediately.