Preheat oven to 375°. Rinse squash & slice down the middle long ways. Remove seeds. Fill a baking dish with 1/2 inch of water. Place squash face down in water & bake for 20 minutes.
Meanwhile, prepare your meatloaf mixture. Fry onion in olive oil until tender. Place in a medium bowl along with chicken, mustard, egg, cheese, oatmeal, garlic powder, sage, & parsley. Mix together with clean hands until well blended.
When 20 minutes is up on the squash remove from oven & drain water from baking dish. Turn squash over & sprinkle with salt & pepper. Spoon meatloaf mixture into squash. Sprinkle again with salt & pepper.
Bake for another 35 minutes OR until an internal temperature of 165° is reached. Enjoy!