Pre-heat the oven to 375 degrees. Cut the acorn squash in half and scoop out the seeds and goopy flesh.
Fill a shallow pie pan with a few inches of water. Place the acorn squash in the water, flesh-side down. Bake for 30 minutes, or until fork tender.
Meanwhile, heat the oil in a large non-stick pan. Sautee the garlic, onions, and mushrooms until fragrant.
Season the raw turkey with the sage, pepper, salt, garlic salt, chili powder, and cayenne. Using your hands, or a large spoon, mix the seasonings into the raw meat.
Add the seasoned ground turkey to the pan and cook, breaking into small pieces as it cooks. Drain the fat from the meat and return to the pan to keep warm.
Once the acorn squash is cooked, remove from the pan of water and lightly season with salt and pepper.
Add a bit of butter if desired. Fill the cavity of the squash with the turkey mixture and serve.