Dice onion and set aside.
Dice garlic and set aside.
Cut pepperoni slices into 4 pieces and set aside.
Spray casserole dish with cooking spray.
Preheat oven to 450°.
Cut off stems of bell peppers and gently remove the seeds and membrane inside the peppers.
Cut peppers in half and set into casserole dish.
Heat large skillet over medium heat and add oil.
Add onion to skillet and sauté onion for 7 minutes until translucent.
Add garlic to skillet and sauté for 1 minutes.
Add ground turkey to skillet and cook until browned, breaking up into small pieces. Season with salt and pepper.
Add tomato paste and mix until well combined.
Add Italian seasoning and red pepper flakes and mix until well combined.
Add 1 cup tomato sauce and mix until well combined. Let cook for 4 minutes then remove from heat.
Spoon the turkey mixture into the red bell peppers in the casserole dish.
Spread ½ cup tomato Sauce over top of turkey mixture.
Pour ½ cup of water into the bottom of the casserole dish. Cover the casserole dish with foil
Bake for 35 minutes until the pepper skins are slightly tender.
Remove from oven.
Sprinkle ½ cup mozzarella cheese on top of peppers, then layer
Sprinkle with a little bit of cheese.
Layer 8 pieces of pepperoni on top of the cheese, then sprinkle remainder cheese on top.
Bake for 10 minutes.
Remove from oven and garnish with fresh basil.