In a large mixer bowl cream butter, honey, brown sugar, egg whites and vanilla. Set aside. In large bowl combine oats, flour, cinnamon, nutmeg, soda and salt. Add oat mixture gradually to margarine mixture. Mix well. Stir in banana and walnuts. Spread dough in a 13 x 9 x 2" baking pan coated with vegetable oil cooking spray. Bake at 350°F for about 25 minutes. Cool completely before cutting. Serve with honey.