In a large mixing bowl, combine rolled oats, peanut butter, honey, and cocoa powder. Mix thoroughly until everything is well incorporated into a thick mixture.

Line an 8-inch square baking dish with parchment paper and transfer the oat mixture into the dish, pressing down firmly.

In a microwave-safe bowl, add chocolate chips and heat in 30-second increments, stirring until melted. Pour the chocolate over the pressed oat mixture.

Cover the dish with plastic wrap and refrigerate for at least 2 hours until the topping has set.

Once chilled, remove bars using the parchment overhang and slice into desired sizes.