Set a large dutch oven over moderate heat. Once hot, drizzle in the oil and add the sausage. Use a wooden spoon to break up the sausage and cook until crispy and fully browned, about 8 to 10 minutes. Stir in the onion, garlic, oregano, basil, fennel, and crushed red pepper. Cook for 1 to 2 minutes to soften the onions a bit.
Add the tomato paste and cook for about 30 seconds or so to develop the flavor. Stir in the crushed tomatoes and tomato sauce. Season with a large pinch of salt and black pepper. Bring to a simmer, reduce the heat and cook, stirring often, until the sauce has thickened.
Bring a large pot of water to a boil and season liberally with salt. Add the pasta and cook according to the package directions. Drain and add the cooked noodles to the pot with the sauce along with the parmesan and mozzarella cheese. Stir until well combined and cook over low heat for about 5 minutes to heat everything up and melt the cheese.
Meanwhile, in a small bowl, stir together the ricotta, lemon, parsley, parmesan, basil, red pepper and a pinch of salt and pepper until evenly combined.
To serve, spoon the pasta into bowls and top with a dollop of ricotta mixture along with some parmesan and parsley for garnish. Enjoy!