Grease an 11x7x1-1/2-inch baking pan; set aside.
Prepare gingerbread mix according to package directions. Pour into the prepared baking pan. Bake in a 350 degree F oven for 15 minutes.
Meanwhile, in a small bowl, combine the brown sugar, flour, and cinnamon. Cut in butter or margarine until mixture resembles coarse crumbs. Stir in the chopped walnuts. Sprinkle over the gingerbread.
Bake for 10 to 15 minutes more or until a toothpick inserted near the center comes out clean. Cut the warm gingerbread into squares. Serve with some whipped cream, if you like. Makes 12 to 15 servings.