Meanwhile, sauté chopped onion and sliced sausage in hot oil in a large nonstick skillet over medium-high heat 4 minutes or until tender. Add minced garlic, and sauté 1 minute. Add tomatoes, and bring to a boil; cover, reduce heat to low, and simmer, stirring occasionally, 20 minutes. Add spinach and basil; cook 5 more minutes.
Place pasta in a large bowl. Add onion mixture, and toss to combine. Sprinkle with Parmesan cheese, if desired.