Preheat oven to 350 degrees.
In the bowl of a standing mixer, add the butter, sugars and vanilla. Using the paddle attachment, cream on medium speed until smooth and fluffy, about 3 minutes.
Add the eggs slowly, one at a time, mixing in between each addition.
In a large bowl, add the flour, baking soda, baking powder, salt and whisk together to combine. Add these dry ingredients to the butter mixture and mix on low, just until all of the dry ingredients and butter are incorporated. Scrap the sides with a rubber spatula to make sure you have gotten all of the butter mixed in.
Once completely mixed, add the oats and chocolate chips and mix slowly to combine.
Spray a 9"x13" baking dish with pan spray. Remove the dough from the mixing bowl and pat it evenly into the bottom of the prepared baking dish.
In a ziplock bag, use a hammer, rolling pin or meat tenderizer to crush the Cadbury Mini Eggs. You'll want them to be in large chunks so it looks like hatched eggs. Sprinkle them over the top of the cookie bar dough evenly.
Bake at 350 for 25-30 minutes, or until golden brown.
Remove from the oven and cool for at least 10 minutes before cutting into bars. Enjoy!