Combine melted butter, graham cracker crumbs, rolled oats, powdered sugar, and peanut butter in a large bowl. Mix well and press the dough into an appropriately sized baking dish or square container. (you can use plastic wrap to push the mixture down)
In a microwave safe bowl, melt the chocolate chips in a microwave on high for 1 minute. Stir. Return to the microwave and heat for 20 seconds, stir and repeat the process until chocolate is melted and smooth.
Spread melted chocolate over the peanut butter mixture. Allow it to cool completely before cutting into squares. (you can allow them to cool at room temperature or in the refrigerator for quicker results).