In large mixing bowl, mix flour, oats, sugar, pecans, baking soda and butter. Mix at low speed until crumbly. Reserve 1.5 cups of mixture for topping; press remainder into bottom of 9 X 13 X 5 cm baking pan. Bake at 180ºC 12-15 minutes. Spoon pie filling evenly over crust. Sprinkle marshmallows and remaining crumbs over top. Return to oven 25 to 35 minutes more, or until topping is golden. Cut into bars when cool.