Preheat the oven to 400F. Cut the butternut squash in half, remove the seeds, and place a few cross hatches on the fleshy part of the squash. Coat with 1 tsp melted ghee, sprinkle with a little salt and pepper, and place face down on a prepared baking sheet.
Bake for about 45 minutes, until the squash is easily pierced with a fork.
Meanwhile, prepare the filling. Heat a large cast iron skillet over medium low heat with the remaining ghee. Add the bison, breaking it up with a wooden spoon into small pieces. Season with salt, cinnamon, ginger and pepper. Add in the chopped rosemary and sage.
Turn the heat to low and simmer until the bison is cooked through, about 5-7 minutes. Watch it carefully - bison is much leaner than ground beef, so it will overcook much faster.
When the bison is cooked through, remove from the heat and stir in the balsamic vinegar.
Once the squash is done, fill the halves with the ground beef. Top with chopped walnuts, feta cheese, and more herbs, if you like. Pomegranate seeds would also be an amazing addition here!