Optional toppings: Chopped red onion, chopped parsley and lemon wedges
Place water, broth, lentils, carrots, onion, celery, garlic and oregano in a 6-qt. electric pressure cooker. Lock lid; close pressure-release valve. Adjust to pressure cook on high for 15 minutes. Let pressure release naturally for 10 minutes; quick-release any remaining pressure.
Stir in spinach, tomato sauce, olives, vinegar, salt and pepper. If desired, serve with red onion, parsley and lemon wedges.
Freeze option: Freeze cooled soup in freezer containers. To use, partially thaw in refrigerator overnight. Heat through in a saucepan, stirring occasionally; add broth if necessary.