Preheat the oven to 400 degrees. Place the peppers in a lightly oiled Pyrex casserole dish, season with salt and bake for 25 minutes or fork tender. Remove peppers, drain any water that has expelled from the peppers and set aside. Saute onions and mushrooms till golden. Add roast beef, Worcestershire, salt
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Use an ice cream scoop to spoon mixture into partially cooked pepper halves. Top with remaining shredded cheese. Bake at 400 for 20-25 minutes or until golden.