Preheat oven to 375 F (190 C). Prepare 9″ x 13″ baking pan.
Stir together flour and sugars in medium bowl.
Cut in margarine until mixture resembles coarse crumbs. Stir in oats and nuts.
Reserve 3/4 cup crumb mixture.
Press remaining crumb mixture onto bottom of baking pan. Bake for 15 minutes.
Beat cream cheese, egg, juice and peel in a small mixing bowl at medium speed with electric mixer until well blended. Pour over crust and sprinkle with reserved crumb mixture.
Return to oven and bake another 25 minutes. Cool completely before cutting into bars.