Add parsnips, apples and shiitakes to the pan and cook, shaking the pan occasionally, until the vegetables begin to soften, about 2 minutes. Add vinegar and stir to scrape up any browned bits. Add broth and simmer over medium heat until the vegetables are tender and the sauce has reduced, 8 to 10 minutes. Stir in sage. Spoon the vegetables and sauce over the turkey and serve.