Preheat oven to 375 degrees. Grease a 9×13-inch pan with nonstick cooking spray.
Spread the pie filling on bottom of pan; next, the drained pineapple chunks.
In a medium mixing bowl, add the dry brownie mix and melted butter. Mix together (will be clumpy).
Sprinkle the cake mix mixture on top of the fruit.
Toast the walnuts, then sprinkle them on top of the brownie mix.
Bake 50 minutes until bubbly and crispy.
Serve warm with whipped topping or ice cream.