Melt butter; add green pepper, mushrooms and peas. Cover and simmer 5 minutes. Remove vegetables with slotted spoon. Add flour to butter, cooking and stirring until smooth. Add half-and-half and cream of mushroom soup, stirring until smooth and thickened. Add tuna, pimiento, mushrooms, green pepper,peas and seasonings. Adjust seasonings to your taste, serve over noodles, biscuits, or toast.