One-Pot Spinach, Chicken Sausage & Feta Pasta

•  2 tablespoons extra-virgin olive oil
• 3 links cooked chicken sausage (9 ounces), sliced into rounds
• 1 cup diced onion
• 3 cloves garlic, minced
• 1 (8 ounce) can no-salt-added tomato sauce
• 4 cups lightly packed baby spinach
• 6 cups cooked whole-wheat rotini
• ¼ cup chopped pitted Kalamata olives
• ¼ teaspoon salt
• ¼ teaspoon crushed red pepper
• ¼ cup water, plus more as needed
• ½ cup finely crumbled feta cheese
• ¼ cup chopped fresh basil

1. Heat 2 tablespoons oil in a large straight-sided skillet over medium-high heat. 
2. Add sliced sausage, 1 cup onion and minced garlic; cook, stirring often, until the onion is starting to brown, 4 to 6 minutes. 
3. Add 1 (8-ounce) can tomato sauce, 4 cups spinach, 6 cups cooked pasta, ¼ cup olives, ¼ teaspoon salt and ¼ teaspoon crushed red pepper; cook, stirring often, until the mixture is bubbling and the spinach is wilted, 3 to 5 minutes. 
4. Add ¼ cup water, or more as needed, to reach desired consistency. 
5. Stir in ½ cup feta and ¼ cup basil.