While pasta water is coming to a boil, heat marinara in a medium saucepan over medium-low heat. Stir in yogurt, add in spinach, and let cook until spinach is wilted. Taste and add salt if needed. If your sauce has lost some flavor, add in 1/4 teaspoon garlic and/or onion powder. Taste and adjust if needed. If sauce is tasting too tangy, add in 1 teaspoon of sugar. Keep over low heat. Stir in cooked tortellini and serve hot.
