Preheat the oven to 375 degrees. Cut the tops off the bell peppers and scoop out the seeds and membranes. Use a small knife to carve simple jack-o'-lantern faces on the front of each pepper.

Place the carved peppers in a baking dish. Set the tops aside for later if desired.

Heat a large skillet over medium heat. Add the ground beef and cook until browned, breaking it up with a spoon as it cooks. Drain any excess fat.

Stir the cooked rice, marinara sauce, garlic powder, salt, and black pepper into the skillet with the beef. Cook for 2 to 3 minutes until everything is heated through and well mixed.

Remove the skillet from the heat and stir in 3/4 cup of the shredded cheddar cheese until melted and combined.

Spoon the filling evenly into the carved peppers. Sprinkle the remaining 1/4 cup cheese over the tops.

Bake for 20 to 25 minutes until the peppers are tender and the cheese is melted and lightly golden.