Depending on how many bars you need and/or the size of bars you want, use 16 or 20 Reese's Hearts. Unwrap Reese's Hearts and place in a bowl. Put the bowl in the refrigerator while you are preparing and cooking the cookie bars.
Preheat the oven to 350 degrees. Lightly grease a 9X13-inch baking pan with cooking spray or line with tin foil or parchment paper. Set aside.
In a small bowl, whisk together the flour, baking soda, salt and oats.
Add the dry ingredients into the wet and mix just until combined.
Add chocolate chips and stir with a wooden spoon.
Take the Reese's Hearts out of the fridge and gently press them on top of the cooked bars. Let the bars cool completely, about 20-30 minutes.