Use a 6-quart slow cooker. Put the chicken into the bottom of the slow cooker insert and add the onion and garlic. Toss the cauliflower and zucchini on top, and pour in the can of tomatoes. Add all dry spices and stir in the chicken broth, taking care not to crumble the cauliflower. Cover and cook on low for 6-8 hours, or on high for about 5 hours.