Preheat oven to 350 F. Line a tray with parchment paper.
Scrub the sweet potatoes well, and poke holes into them. Rub with 2 teaspoons of oil, sprinkle with ¼ tsp salt and roast for 1 hour or until very tender when you piece them with a fork. Once cool enough to touch, cut them in half lengthwise and scoop out the insides into a bowl, leaving a thin shell around the edges.
While the potato is roasting, heat two teaspoons of oil and the butter in a large skillet over medium low heat. Add in the onions and coat them in the oil. Stirring every 5 minutes, let the onions cook until it reaches a caramelized amber colour, about 40 to 50 minutes. Add in the balsamic, thyme, and a pinch each of salt and pepper to taste. Set aside. Set aside.
Finally, add the turkey sausage to a small skillet with 1 teaspoon of oil and break up the meat into small pieces. Cook until well browned then set aside.
In a bowl, mix the sweet potato insides with the cinnamon, maple syrup, caramelized onion, cooked turkey, diced apple, ½ cup Swiss cheese, ¼ cup Parmesan cheese and salt and pepper, to taste.
Stuff the sweet potato shells with the mixture, then top with pecans, ¼ cup of swiss cheese and 2 tablespoons of parmesan cheese. Place them in the oven for about 10 to 15 minutes until the skin gets lightly crispy and the mixture warms through.