In a large skillet, cook ground beef, bell peppers, onion, and garlic over medium heat until beef is browned and crumbly. Drain, if needed. Add oregano, salt, and pepper.
Stir in tomato paste and sauté until fragrant, about 2-3 minutes. Add rice, diced tomatoes, and water; stir to combine. Bring mixture to a boil, reduce heat to low, cover and simmer 40 minutes.
Remove from heat but keep covered an additional 5-10 minutes. Fluff the rice with a fork to separate.
Serve in bowls, and top with shredded cheddar cheese.