Wash the bell peppers, cut off the tops, and scoop out the seeds.

In a skillet over medium heat, brown the ground meat until fully cooked. Drain excess fat and add chopped onions; sauté until translucent.

In a bowl, mix the cooked meat with uncooked rice, tomato sauce, garlic powder, oregano, salt, and pepper until well combined.

Generously stuff each bell pepper with the filling mixture.

Place stuffed peppers upright in a slow cooker and pour any remaining tomato sauce over them.

Cover and cook on low for 6 hours or until peppers are tender. Serve warm.