In a food processor, pulse the tomatoes, peanut butter and garlic. Transfer to a slow cooker.
Add in the sweet potatoes, chickpeas, vegetable broth, crushed red pepper flakes, salt and pepper. Cover and cook on low for 6-8 hours, or until the sweet potatoes are tender.
Mix in the spinach and transfer to bowls. Serve with peanuts on top, if desired.