Preheat a grill to high. Mix 2 tablespoons apple jelly with the thyme. Season the pork chops with salt and pepper and brush with olive oil on both sides. Grill the chops until marked, about 3 minutes per side. Brush with the jelly-thyme mixture and continue to grill until the chops are cooked through, about 2 more minutes. Set aside to cool.
Soak the diced onion in a bowl of cold water, about 10 minutes. Meanwhile, whisk the mustard, vinegar and the remaining 1 tablespoon apple jelly in a large bowl and season with salt and pepper. Slowly add 1/2 cup olive oil, whisking until smooth.
Cut the pork into bite-size pieces and drain the onion. Add the lettuce, apple, turnip, pork, onion and blue cheese to the bowl with the dressing and toss. Top with parsley, if desired.