Bring a large pot of lightly salted water to boiling. In a large skillet, heat oil over medium heat. Add peppers and sauté for 5 minutes, stirring. Add tomatoes, garlic, red-pepper flakes, onion flakes, salt and black pepper. Simmer for 10 minutes.
Stir in tomato paste and cook for 5 more minutes. Meanwhile, cook tortellini in boiling water as package directs. Drain; toss with sauce. Serve with Parmesan, if desired. Makes 6 servings.