1Spray 5- to 6-quart slow cooker with cooking spray. In 10-inch skillet, heat oil over medium-high heat. Cook onion in oil 2 minutes, stirring frequently, until tender. Add garlic and tomato paste; cook 1 minute. Spoon mixture into slow cooker. Stir in remaining ingredients except spinach.
2Cover; cook on Low heat setting 9 hours. Discard bay leaves. Stir in spinach just before serving.