Cut tops of bell peppers and rinse in cold water; remove seeds and cut away white ribs. Chop the edible parts of tops and set aside. Place peppers in a large pot and cover with salted water.
Bring to a boil; reduce heat cover and simmer for 5 minutes. Drain and set aside.
Heat olive oil and butter in large skillet over medium heat until the oil is hot and butter is foamy. Saute chopped bell pepper, chopped onion, and chopped celery for about 5 minutes, or until vegetables are tender.
Add (undrained) canned diced tomatoes, tomato sauce, crushed garlic, oregano, basil, 1 teaspoon of the salt, and 1/4 teaspoon of the pepper. Bring to a simmer and cook for about 10 minutes.
In large mixing bowl, combine egg with remaining 1 teaspoon salt, 1/4 teaspoon pepper and Worcestershire sauce. Gently stir to blend; add ground beef, cooked rice, and 1 cup of tomato sauce mixture. Mix well.
Heat oven to 350º
Stuff peppers loosely with ground beef mixture and place in 13X9X2 baking pan. Pour remaining tomato mixture over stuffed peppers.
Bake for about 45 minutes, or until meat mixture is thoroughly cooked.
Optional: Top stuffed peppers with small amount of shredded cheddar cheese just before they are done and return to oven just until cheese melts.