Drain mushrooms and reserve juice. Cook and stir drained mushrooms and green pepper in butter over heat 5 minutes; remove from heat.
Blend in flour, salt and pepper. Cook over low heat, stirring constantly, until mixture is bubbly; remove from heat.
Stir in instant bouillon, milk, water and reserved mushroom liquid. Heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in chicken, pimiento and peas if used; heat through. Serve over Minute Rice, toast, or noodles.