Melt 4 tablespoons of the butter over high heat in a large 6 qt. dutch oven or stockpot. Add the diced turkey breast and cook until the turkey browns, about 5 minutes. Remove the turkey from the pan and set it aside. Reduce the heat to medium and add the remaining 4 tablespoons of butter. When melted, add the onion, celery, red pepper, and garlic. Cook for about 5 minutes until the vegetables soften, stirring occasionally.