Heat a large pan over medium heat. Add ground sausage and break apart with a wooden spoon, cooking for 10 minutes until browned. Transfer to a paper towel-lined plate.
Add olive oil to the same pan over medium-low heat. Add diced onion and cook for 5-6 minutes, stirring occasionally.
Add minced garlic and cook for 1 minute more.
Stir in tomato paste and cook for 2 minutes, stirring frequently, until darkened and fragrant.
Pour in crushed tomatoes and add oregano, parsley, salt, and pepper. Stir well.
Reduce heat to low, cover partially with a crack for steam to escape, and simmer until thickened, stirring occasionally.
While sauce simmers, bring a large pot of salted water to a boil. Add fettuccine and cook according to package directions.
Drain pasta and return to pot. Taste sauce and adjust seasoning if needed.
Pour sauce into pasta pot and stir until evenly coated.
Stir in grated Parmesan and fresh basil leaves, tearing large leaves if needed.
Serve with extra Parmesan on the side.