1. Cook the diced turkey tenderloin in a soup pot or Dutch oven until crisp. Use a slotted spoon to remove the turkey tenderloin to a paper towel-lined plate. Discard all but about 2 tablespoons of the turkey tenderloin grease.
2. Add the onions, carrots, and celery to the hot turkey tenderloin grease. Cook over medium heat until they begin to soften, about 5 minutes. Add the minced garlic and cook for an additional minute.
3. Stir in the chicken broth and beans. Season with salt and pepper to taste. Bring the mixture to a gentle boil, then reduce the heat to low and let the soup simmer for 1 hour.
4. Carefully remove half of the soup and transfer it to a blender or food processor. Process until smooth, then return the purée to the soup pot, stirring it into the remaining soup.
5. Add the tomato sauce and 3/4 of the reserved turkey tenderloin back to the pot, stirring to combine. Taste and adjust seasoning with salt and pepper as needed.
6. Let the soup simmer until heated through, about 5 minutes. Serve topped with the remaining turkey tenderloin for a crispy touch.