Preheat the oven to 375 degrees. Slice the tops off the bell peppers and scoop out the seeds and membranes. Carve simple jack-o'-lantern faces into the sides of each pepper.
Place the peppers upright in a baking dish. Set aside while you prepare the filling.
Heat a large skillet over medium heat. Add the ground turkey, chopped onion, and minced garlic. Cook until the turkey is no longer pink, breaking it up as it browns.
Stir in the cooked rice, marinara sauce, oregano, salt, and black pepper. Let the mixture simmer for 3 minutes so the flavors combine.
Spoon the turkey and rice mixture evenly into the carved peppers. Top each one with shredded mozzarella cheese.
Bake for 25 minutes until the peppers soften and the cheese melts and turns lightly golden. Sprinkle with fresh parsley before serving.