In a large bowl, cream butter and brown sugar until light and fluffy. Combine the flour, cinnamon and baking soda; gradually add to creamed mixture and mix well. Stir in the oats, coconut and nuts. Remove 1 cup for topping.
Press remaining oat mixture into an ungreased 13-in. x 9-in. baking dish. Bake at 350° for 12-13 minutes or until light brown. Cool on a wire rack.
In a large bowl, fold whipped topping into yogurt. Spread over crust. Sprinkle with reserved oat mixture. Cover and refrigerate for 4 hours or overnight.