To prepare a turkey tortilla soup, you'll first need to prepare your ingredients. To do this, first you will need: 1 pound ground turkey, 1 cup chopped onion, 2 tablespoons chopped celery, 1/2 cup diced green bell pepper, and 1 tablespoon dried oregano. You will also need 2 cups of water. Bring the water to boil, then add the turkey and onion mixture to the pot. Cook the mixture over medium-low heat, stirring occasionally, until the onions are translucent, about 15 minutes. Then add in the tomatoes, tomato paste, sour cream, cumin, salt and pepper to taste. Cover the soup with cling wrap and refrigerate until you are ready to serve.