Preheat oven to 375°F. In large bowl, combine 3 cups stuffing mix with 2 cups stock. Let soften.
Melt butter in pan over medium heat. Cook onions, celery, garlic until soft. Add Bell's Seasoning. Cool slightly.
Process remaining cup of stuffing into fine crumbs. Mix ground turkey, eggs, salt, and pepper into soaked stuffing. Fold in cooled vegetables and crumbs.
Line sheet pan with parchment and spray. Shape mixture into loaf with wet hands. Bake 55-60 minutes to 155°F internal temperature. Rest 15 minutes.
For gravy: Melt butter, whisk in flour. Cook 2-3 minutes. Gradually whisk in hot stock. Add Kitchen Bouquet. Simmer until thickened.