Step 1Cook pasta in boiling salted water according to directions until al dente.
Step 2Prick sausage with fork and brown in nonstick skillet over medium-high heat, turning as necessary, about 4 minutes. Drain on paper towels. Cut into thin slices (remove casing if tough).
Step 3Wash out skillet. Add sliced sausage, Ratatouille and marinara sauce. Bring to simmer. When pasta is cooked, reserve 1 cup cooking liquid. Drain pasta; add to skillet along with cheese and some of reserved cooking liquid. Toss well. Taste and adjust seasoning and add more liquid if pasta seems too dry. Serve hot with additional cheese on the side.