Cut off tops of peppers. Scoop seeds from cavities. Heat oil in heavy large skillet over medium-high heat. Add onions, garlic, thyme and oregano. Sauté until onions soften, about 8 minutes. Transfer to large bowl. Mix in rice, turkey, 1/2 cup tomato sauce, egg, salt, pepper, and allspice. Cool 10 minutes.
Fill pepper cavities with beef mixture. Stand filled peppers in single layer in heavy large pot. Pour remaining 2 cups tomato sauce around peppers. Bring sauce to boil over medium-high heat. Reduce heat to medium-low, cover pot and simmer 20 minutes. Spoon some sauce over each pepper. Preheat oven to 350 degrees. Transfer peppers to a pyrex dish, cover with foil, and cook for 20 more minutes. Serve with leftover sauce.