Preheat the oven to 375 degrees. Rinse squash, slice in half and place face down on a well-oiled baking sheet. Bake approximately 45 minutes until tender. Place rice and 4 cups of water in a pot and boil. Cover reduce heat, simmer and cook until soft, approximately 50 minutes. Drain well. While squash and rice are cooking, place oil in a large pan on medium high heat. Add onion, celery, garlic and cook for 5 minutes, stirring frequently. Add remaining ingredients and cook for 5 minutes, stirring frequently. Add water to prevent sticking. Place in a large bowl with drained rice and mix well. Stuff into squash and bake for 10 minutes.