Preheat the oven to 375 degrees. Cut the tops off each bell pepper and scoop out the seeds. Use a small knife to carve simple jack-o'-lantern faces on the sides.
Place the carved peppers in a baking dish. Set the tops aside if you want to use them for serving.
Heat a skillet over medium heat. Add the ground turkey, diced onion, and minced garlic. Cook until the turkey is browned and the onion is soft.
Stir in the cooked rice, tomato sauce, salt, and black pepper. Mix well and remove the skillet from heat.
Spoon the filling evenly into each carved pepper. Sprinkle the shredded cheddar cheese over the top of each one.
Bake for 25 minutes until the peppers are tender and the cheese is melted.