The tomatoes are added right before serving; otherwise, their acid would prevent the peas from getting tender. The kale, a favorite super-food to use in soups and winter salads, also goes in at the end in order to keep its vibrant, green color. Like many slow-cooker soups and stews, this recipe is substitute-friendly swap out the turkey sausage for pork or chicken sausage and use your favorite frozen pea or bean instead of the black-eyed peas.