In a large heavy bottom pot over medium heat add olive oil.
Add onions, carrots, celery, and mushrooms, dried thyme, parsley, and sprinkle with a little salt. Saute for 4-5 minutes, until veggies are softened and onions are translucent.
Add 3 cups of broth and the mashed potatoes and stir until the potatoes are mostly dissolved and the broth is smooth.
Add diced turkey and add another cup of broth a little at a time, if you want your soup thinner.
Bring everything to a simmer and reduce heat to medium-low and cook until heated through, about 15-20 minutes. Stir occasionally and season to taste with salt and pepper.