Line an 8x8 inch square baking pan with parchment paper.

In a large bowl, mix the graham cracker crumbs, melted butter, and powdered sugar until a sandy dough forms.

Press the crumb mixture firmly into the bottom of the prepared pan in an even layer.

Heat 1 cup of peanut butter in the microwave for 30 seconds until spreadable, then pour it over the crust and smooth with a spatula.

Refrigerate the pan for 30 minutes to allow the peanut butter layer to set.

In a microwave-safe bowl, combine the chocolate chips, the remaining 1/2 cup of peanut butter, and the vegetable oil.

Microwave the chocolate mixture in 30-second intervals, stirring until completely smooth.

Pour the chocolate mixture over the chilled peanut butter layer and spread evenly.

Refrigerate for at least 2 hours until firm.

Lift from the pan using the parchment paper and cut into bars.