Combine all ingredients except pie filling and marshmallows in large bowl. Beat at low speed, scraping bowl often, until mixture resembles course crumbs. Reserve 1 1/2 cups crumb mixture for topping.
Press remaining crumb mixture into ungreased 13x9-inch baking pan. Bake for 12-15 minutes or until lightly browned on edges.
Gently spoon pie filling over hot, partially baked crust; sprinkle with marshmallows. Sprinkle with reserved crumb mixture. Continue baking 25-35 minutes or until lightly browned. Cool Completely. Cut into bars.