Preheat oven to 350 F. Spray a 9x9 inch baking dish with pan release spray and set aside.
Wash peppers and cut the tops off, removing all steeds and inner membranes.
Fill a large saucepan with water and bring to a boil. (Add enough water to the sauce pan so that peppers will be completely covered when placed inside).
Add peppers into the boiling water and push down so that they are completely submerged. Boil for 5 minutes, remove from heat and drain.
Stuffed Pepper Filling
Combine the ground chicken, chopped onion and minced garlic in a medium sauce pan. Cook over medium heat until chicken is cooked (it should be 165F).
Drain any excess liquid or fat from the chicken. Set aside.
In a large bowl, combine the cooked chicken, cooked brown rice, Italian seasoning, onion powder, garlic powder, tomato sauce and Parmesean cheese. Mix until combined.
Stir in 1 cup of the shredded Mozzarella cheese and mix until combined.
Stuffing the Peppers
Set the par-boiled peppers upright in your prepared baking dish. (Sometimes it helps to lean them up against one another so they stand upright).
Take the prepared stuffing mixture and fill each pepper to the very top. (Use your spoon to make sure the stuffing fills all areas inside the pepper).
Top peppers with the remaining mozzarella cheese.
Bake in preheated oven for 20 minutes.
After 20 minutes, turn oven up to Broil setting, and bake for 2 more minutes.