Rinse and pat the turkey thighs dry with paper towels, then sprinkle with salt and pepper. In a shallow bowl, mix the flour with poultry seasoning until well combined.
Heat the olive oil in a large skillet over medium-high heat; dredge the turkey thighs all over with the seasoned flour, shake off excess flour, then cook the turkey thighs in the hot oil until the meat is browned, about 5 minutes per side.
Stir the onion, mushrooms, and garlic into the pan. Stir until the mushrooms have begun to give up their juice and the onions are translucent, about 5 minutes. Whisk the chicken broth, cream of chicken soup, and sherry together in a bowl, and stir in the oregano, parsley, and garlic powder. Pour the mixture over the turkey thighs. Cover the pan, reduce heat to medium-low, and simmer until the turkey meat is no longer pink inside and the juices run clear, about 30 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Slice the turkey thighs, and serve with sauce.
