Heat olive oil in a large skillet over medium-high heat. Add chicken sausage, breaking it up as it cooks until browned (8-10 minutes). Remove and set aside.
In the same skillet, sauté the chopped onion for about 5 minutes until softened. Then add minced garlic, cooking for another minute until fragrant.
Stir in crushed tomatoes, tomato sauce, dried oregano, basil, salt, and pepper. Simmer covered for at least 30 minutes.
Cook pasta according to package directions in salted water. Reserve 1 cup of pasta water before draining.
In a separate skillet, melt butter over medium heat and add more minced garlic; cook until fragrant.
Combine cooked pasta with the garlic butter and sausage sauce; adjust consistency with reserved pasta water if needed. Finish with fresh parsley.