3. Step
Meanwhile, heat 2 tablespoons oil in a large skillet over medium heat. Add onion and cook, stirring, until starting to soften, about 3 minutes. Add tomatoes, garlic powder, basil, oregano, salt and crushed red pepper; bring to a simmer. Cook, stirring, until thickened, about 5 minutes. Stir in chicken and the cooked rotini. Transfer to the prepared baking dish and top with mozzarella.