Combine oats, 1 cup flour, and sugar in a large bowl.
Cut in margarine with a pastry blender until mixture resembles coarse meal. Press one-half of oat mixture into bottom of a 9-inch square pan coated with cooking spray.
Bake at 350 for 15 minutes.
Remove from oven; sprinkle walnuts over prepared crust.
Combine syrup and remaining 1/4 cup flour; stir well.
Pour syrup mixture over nuts.
Sprinkle remaining oat mixture over syrup mixture.
Bake at 350 25 to 30 minutes or until golden.
Let cool in pan on a wire rack. Cover and chill at least 1 hour.