Preheat oven to 350 degrees F.
Spray a 9x13 baking pan with cooking spray (makes the paper stick to the pan) then line the pan with parchment paper (allow the edge of the parchment paper to extend past the ends of the pan to create 'handles' that make removal of the cookie bars easy) and spray the parchment paper with cooking spray.
In a large bowl, stir together cake mix, eggs, and oil until thoroughly mixed. The mixture is thick.
Evenly press the dough mixture evenly in the lined 9x13 pan.
Bake for 15-20 minutes until the cookie bars are baked through and lightly browned at the edges. Don’t overbake.
Allow cookie bars to cool and then use the 'handles' to gently lift the bars onto a flat surface.
Spread about ½ the frosting onto the warm bars, or melt the frosting in a microwave-safe bowl for about 20-30 seconds until runny and drizzle over cooled cookie bars. Immediately sprinkle sprinkles on top of the frosting. An entire can of frosting can be used if you love a lot of frosting.
Allow frosting to cool and harden, then cut into bars.