Preheat the oven to 375°F (190°C).
Cut the tops off the bell peppers and remove the seeds and membranes. Set aside.
Heat olive oil in a large skillet over medium heat.
Add the chopped onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet and cook until browned, breaking it up with a spoon, about 6-8 minutes.
Stir in the cooked rice, diced tomatoes, dried oregano, dried basil, salt, and black pepper. Cook for 2 minutes to combine flavors.
Remove the skillet from heat and stir in half of the shredded cheddar cheese.
Stuff each bell pepper with the beef and rice mixture, pressing down gently to fill completely.
Place the stuffed peppers upright in a baking dish.
Sprinkle the remaining shredded cheddar cheese evenly over the tops of the stuffed peppers.
Cover the baking dish with aluminum foil and bake for 30 minutes.
Remove the foil and bake for an additional 10 minutes until the cheese is melted and bubbly.
Remove from the oven and let cool for 5 minutes before serving.