In medium mixing bowl, stir graham crackers, butter and brown sugar until evenly moistened. Press into bottom of 9-by-13-inch oven-safe dish. Refrigerate.

In large mixing bowl, combine pumpkin, marshmallow fluff and pumpkin spice. Use hand-mixer to beat until just combined.

Using spatula, fold whipped topping into filling. Pour filling over crust and smooth evenly. Cover and refrigerate 3 hours.

Turn oven to broil. Top pie with mini marshmallows and chocolate chips in single layer and broil 2-3 minutes, until marshmallows are toasted. Allow pie to cool 10 minutes before slicing into squares.