Preheat the oven to 400°F and line a cookie sheet with parchment paper. Slice the squash in half (see safety instructions) and scoop out the seeds with a metal spoon or fork.

Turn the squash cut side down on the cookie sheet, and place in the preheated oven. Bake for 20 minutes, or until fork tender.

While the squash is baking, saute the ground sausage in a large skillet on the stove, breaking it apart into crumbles as it cooks. Once the sausage is fully cooked, remove it from the pan and set aside.

In the same pan, heat the olive oil and saute the onions until softened, 4 or 5 minutes. 

Add the kale, garlic, celery, apples, and herbs, cooking for an additional 4 or 5 minutes, to allow the flavors to meld together. Add the sausage back to the skillet, and stir to combine.

Remove the cooked squash from the oven, and use a spoon to scoop some of the flesh away from the rind. Chop the flesh and add it to the filling on the stove. Taste the filling for seasoning and adjust as needed.

Fill each squash until heaping full. Place the filled squash back into the oven, and bake for 15 minutes.

Take the squash out of the oven, and sprinkle each half with feta cheese and chopped nuts. Bake 5 minutes more. Serve hot.