Preheat oven to 400 degrees, and line a quarter-sized baking sheet (12 x 8 x 1 inch) (or other oven-safe baking dish) with aluminum foil.
Evenly spread cauliflower rice onto baking sheet, and roast for 20 minutes.
Reduce oven temperature to 380 degrees.
While the cauliflower is cooking, wash the outside of the pumpkin with water to remove any dirt or debris. Hollow out the pumpkin reserving the lid**. Set aside.
In a large saute pan, heat oil and add celery, onion, and ground beef. Cook for about 6-8 minutes until beef is browned and cooked through.
While the beef and onion mixture is cooking, add cream cheese and butter to a small sauce pan. Heat over medium heat whisking continuously until butter melts and cream cheese is softened. (Mixture may appear curdled.) Add chicken stock, garlic powder, salt, pepper, soy sauce, and brown sugar. Whisk until smooth, and continue to simmer for 10-15 minutes until sauce begins to thicken.
To a large mixing bowl, add browned beef mixture, roasted cauliflower rice, water chestnuts, and prepared sauce. Mix until combined.
Place pumpkin on the aluminum foil lined baking sheet. Add 1/3 of shredded cheese to bottom of pumpkin. Next, add 1/2 of filling mixture and an addition 1/3 of shredded cheese. Top with remaining 1/2 of filling mixture and last of cheese. (Do not overfill pumpkin). Add pumpkin lid on top of pumpkin, slightly ajar, allowing steam to escape.
Bake for 1 hour, or until pumpkin is tender.***
Portion out servings of the filling while scraping out sides of the pumpkin.
Add additional salt and pepper to taste, and enjoy!