Preheat oven to 375 degrees F.
Wash hands with soap and water.
Cut squash in half from stem to tip. Use a sharp knife and a firm grip. Break squash in half and scoop out seeds with a sturdy metal spoon.
Place squash halves, face side up, on a cookie sheet. Spray surfaces with non-stick cooking spray. Roast in oven for 45-60 minutes, until flesh is tender throughout.
Heat a large skillet on stovetop and spray with non-stick cooking spray.
Sauté ground turkey, chopped onions, and red bell pepper until turkey is cooked through (internal temperature should reach 165 degrees F) and vegetables are tender, about 5-10 minutes. Season with black pepper and garlic powder. Add cooked barley.
Stuff squash with ground turkey mixture. Top each with 1/4 cup cheese. Place in oven for 2-5 minutes, until cheese is melted.