Peel onions without cutting off roof end. Cut a slice about 1 inch thick from the top of onion. Place onions in large amount of boiling salted water and cook over moderate heat until tender. Drain and cool. Scoop out center of onions to form cups, leaving a half inch shell. Save centers. Saute green peppers in butter until crisp. Add 1/2 cup of chopped reserved onion centers. Cook for a few minutes in remaining ingredients, except rice. Cook stirring until smooth. Add rice and mix. Fill onions with mixture. Bake in dish for 20 minutes at 350ºF.