Melt butter in a microwave-safe bowl or on the stove, with the wrapping paper removed, in 20-second intervals until fully melted.
In a large bowl, mix together all ingredients for the oat crumble, including the butter, until it comes together.
Line an 8x8 square baking pan with parchment paper.
Press down half of the oatmeal mixture into the bottom of the pan, using a flat spatula to help press it down tightly. Place in the freezer.
In a small pot over medium-low heat on the stove, melt chocolate chips by adding in the filling ingredients.
Constantly stir until melted. Then remove the bars from the freezer and pour the melted chocolate evenly over top, using a rubber spatula to smooth it out.
Take the remaining oat mixture and sprinkle it in an even layer over top of the chocolate filling, gently pressing it down.
Place the baking dish in the freezer for around 6 hours, until fully set.
Once ready, use a pizza cutter to cut into 9 servings. Enjoy!