To prepare a vegetable gumbo crock pot and slow cooker recipe, first you will need to gather your ingredients. You can find these ingredients at most grocery stores, or you can make them at home. Place the chopped onions, celery, bell peppers, and garlic in the bottom of the slow-cooker. Add the vegetable broth, tomato paste, thyme, bay leaf, salt and pepper to taste. Cover and cook on low for 6-8 hours or on high for 7-10 hours.