Chop enough reserved green pepper tops to equal 1/4 cup; discard remaining tops or use for another purpose. Set chopped pepper aside.
Place hollowed-out green peppers in a microwave-safe dish; cover and cook in microwave until bright green and steaming, about 3 minutes. Set peppers aside.
Cook and stir ground beef in a skillet with reserved chopped pepper tops and onion over medium heat until beef is browned, the juices run clear, and the onion is translucent, about 10 minutes; drain excess grease. Pour in diced tomatoes with their juice, rice, water, Worcestershire sauce, salt, and black pepper; bring to a boil. Reduce heat to low, cover skillet, and simmer until rice is tender, about 30 minutes.
Preheat oven to 350 degrees F (175 degrees C).
Stir cheese into ground beef-rice mixture and spoon mixture into precooked peppers. Set peppers upright in an 8x8-inch baking dish.
Bake in the preheated oven until cheese is melted and the peppers are tender, about 30 minutes.