Preheat oven to 350˚F degrees.
Prepare rice according to package directions.
In the meantime, melt butter in a large skillet over medium-high heat.
Add diced onions and celery to the skillet and cook for 3 minutes, or until softened, stirring frequently.
Stir in mushroom slices and garlic; cook for 2 minutes.
Add cubed turkey and mix; remove from heat.
Transfer mushroom mixture, prepared rice, and 1/2 cup shredded cheese to a 2-quart baking dish; stir and set aside.
In a mixing bowl whisk together milk, heavy cream, chicken broth, garlic powder, onion powder, salt, pepper, paprika, and nutmeg; whisk until thoroughly incorporated.
Add milk mixture to the baking dish and mix until everything is completely combined.
Add remaining cheese on top.
Bake for 30 to 35 minutes, or until hot and bubbly.
Remove from oven and let stand 5 minutes.