Cook noodles as directed on package but add frozen peas to cook with them. Mix butter, milk, cheese packet and soup together until well blended. Add drained noodles/peas. Add mushrooms and chicken and gently mix. Pour into 8x8 casserole dish. Sprinkle bread crumbs and shredded cheese atop. Bake at 350° for 20 minutes or until top is golden brown.