Preheat the oven to 375°F (190°C).

Cut the tops off the bell peppers and remove the seeds and membranes.

In a skillet over medium heat, cook the ground beef until browned. Drain excess fat.

Add chopped onion to the skillet and cook until translucent, about 5 minutes.

Stir in cooked rice, diced tomatoes, garlic powder, chili powder, salt, and black pepper. Mix well and heat through.

Remove from heat and stir in half of the shredded cheese.

Stuff each bell pepper with the beef and rice mixture, pressing down to pack it in.

Place the stuffed peppers upright in a baking dish. Sprinkle the remaining cheese on top.

Cover with foil and bake in the preheated oven for 25 minutes.

Remove the foil and bake for an additional 5 minutes, or until the cheese is bubbly and golden.

Let cool for a few minutes before serving.