Heat oven to 350°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 at 350°F. for 30 to 40 minutes or until edges are bubbly. Cool 45 minutes.
To serve, spoon crisp into bowls. Top each serving with ice cream; drizzle with chocolate syrup from packet. Garnish with mint sprigs.