Filling. Heat oven to 350 degrees F. Coat a 13x9x2-inch baking pan with nonstick cooking spray. In a large bowl, combine cake mix, 1 1/3 cups water, the egg whites and oil. Prepare as per package directions. Fold in chopped cookies and pour into prepared pan. Bake at 350 degrees F for 32 to 35 minutes. Cool completely in pan on a wire rack.
Finely crumble cake into a large bowl. Stir in frosting and press together with the back of a spoon. Shape mixture into 1-1/4-inch balls and place on a baking sheet. Refrigerate 2 hours or freeze for 20 minutes.
Coating. Once cake balls are chilled, melt candy as per package directions. Remove a few balls from the refrigerator or freezer. Dip a lollipop stick about 1 inch into the melted candy. Press a cake ball onto the stick, being careful not to press stick too far. Dip ball into desired coating and gently tap so excess coating drips back into bowl. Garnish with contrasting-color drizzle, nonpareils, crushed cookies or a combination of ingredients. Transfer decorated pops to a parchment or wax paper-lined sheet. Repeat, reheating candy melts as needed. Refrigerate for 30 minutes, then store at room temp up to 2 weeks.