Preheat oven to 350 degrees F. Reserve chocolate syrup packet from brownie mix for topping. In large bowl, combine brownie mix, oats and walnuts; mix well. Add butter; stir until mix is moistened. Mixture will be dry.
Spoon pie filling evenly into ungreased 9- or 8-inch square (2 quart) glass baking dish. Sprinkle brownie mixture over pie filling.
Bake for 30-40 minutes or until edges are bubbly. Cool 45 min. To serve, spoon crisp into bowls. Top each serving with ice cream; drizzle with chocolate syrup from packet. Garnish with mint sprigs.