Heat oven to 375'F. Slice tops off peppers and scoop out seeds. Stand peppers in 9" square baking dish. In medium saucepan of boiling salted water, cook rice 7 minutes. Drain, rinse under cold water and drain again. In medium skillet, heat oil. Add scallion, ginger and garlic. Cook over medium-high heat until vegetables are softened and fragrant but not browned, about 1 minute. Transfer to medium bowl. Add ground pork, peas, rice, 2 tablespoons soy sauce, 1 tablespoon sherry, 1/4 teaspoon sugar, 1/4 teaspoon pepper and salt to bowl. Mix gently but thoroughly to avoid crushing peas. Stuff peppers with meat mixture. In 2-cup glass measure, combine beef broth, remaining sherry, soy sauce, sugar and pepper.
Pour sauce over stuffed peppers and cover dish with foil. Bake 45 minutes. Remove foil from dish; reduce oven temperature to 350'F. and continue baking, basting a few times with sauce, 15 minutes. Transfer peppers to serving platter. Place baking dish on top of stove. Dissolve cornstarch in 2 tablespoons water. Whisk into liquid in baking dish, and cook over medium heat until sauce boils and thickens, about 2 minutes. Serve sauce with peppers.