Preheat oven to 350°F.
Combine all ingredients except pie filling and marshmallows in a large bowl. Beat at low speed, scrapping bowl often, until mixture resembles coarse crumbs (mixture will be moist).
Reserve 1 1/2-cups crumb mixture for topping. Press remaining crumb mixture into ungreased 9x13-inch baking pan. Bake for 12 to 15 minutes or until lightly browned on edges.
Remove from oven and gently spoon pie filling evenly over hot, partially baked crust. Sprinkle with marshmallows and reserved crumb mixture. Continue baking for 25-35 minutes or until lightly browned.
Cool completely. Cut into 36 bars.