Wash the orange bell peppers and pat them dry. Carefully slice off the tops (keep them for “lids”). Remove the seeds and membranes from the inside. Using a small, sharp paring knife, carefully carve Jack O Lantern faces into one side of each pepper. Set the peppers and their tops aside.
Heat the olive oil in a large skillet over medium heat. Add the diced onion and cook for about 3 to 4 minutes until it becomes translucent and soft.
Add the ground beef to the skillet. Use a wooden spoon to break the meat into small crumbles. Cook until the beef is fully browned and no pink remains. Carefully drain any excess grease from the pan to keep the filling light.
Stir in the Italian seasoning, garlic powder, salt, and pepper. Add the cooked rice and the marinara sauce. Mix everything together and let it simmer for 2 minutes. Remove from heat and stir in half of the shredded cheddar cheese until it begins to melt.
Preheat your oven to 350°F (175°C). Stand the carved peppers upright in a baking dish. Spoon the meat and rice mixture into each pepper, packing it down gently. Top each pepper with the remaining cheese and place the pepper “lids” back on top.
Add about 1/4 cup of water to the bottom of the baking dish to create steam. Cover the dish loosely with foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes until the peppers are tender but still hold their shape. Serve warm.