Heat oil in a small skillet.Saute garlic and onion for 2 or 3 minutes, then pour into slow cooker.Combine all ingredients except spinach, cilantro, and cauliflower in the slow cooker.Cook on high for 4 hours or on low for 6 to 8 hours.Check occasionally—you may need to add more water or broth.Add cauliflower for the last hour of cooking.Add spinach and cilantro minutes before serving.Season to your liking.