Line the bottom circle of a 9-inch fluted tart pan with a circle of parchment paper. Lightly spray the parchment circle with nonstick spray. Set it aside.

Using a medium-size heat-safe mixing bowl, combine the chocolate chips and vegetable oil. Heat the chips and oil for 45 - 55 seconds in the microwave. Stir until the chocolate chips are completely melted and smooth.

Spoon 0.5 of the melted chocolate into the prepared tart pan. Using a large spoon or offset spatula, evenly spread the chocolate over the bottom and up the sides of the tart pan. Chill the coated tart pan in the refrigerator while preparing the chunky peanut butter filling.

Using a large mixing bowl, whisk together the powdered sugar and graham cracker crumbs. Set it aside.

Using a medium-size heat-safe mixing bowl, add the chunky peanut butter and the butter. Heat in the microwave for 45 seconds. Remove the bowl and stir to thoroughly combine.

Pour the chunky peanut butter mixture over the powdered sugar and graham cracker crumbs. Stir until the mixture is completely incorporated.

Remove the chocolate-coated tart pan from the refrigerator. Using either a silicone spatula or an offset spatula, spread the chunky peanut butter mixture into the bottom of the coated tart pan. Be sure the chunky peanut butter mixture is smooth and even.

Spoon the remaining melted chocolate mixture on top of the chunky peanut butter layer. Use the spoon or an offset spatula to evenly smooth the chocolate all the way to the sides.

Once the remaining chocolate has been spread, gently tap the tart pan to ensure the chocolate settles. Chill in the refrigerator for 4 hours to overnight.

When you are ready to serve, remove the tart pan from the refrigerator. To remove the peanut butter cup from the tart pan, center the pan over a small mixing bowl and apply slight pressure to the edge of the tart pan to encourage the sides to come away. Have a serving platter or 10-inch cake circle ready to place the peanut butter cup pie on.

Gently flip the pie upside down to remove the removable tart pan bottom, and carefully peel off the parchment circle. Place the serving plate or cake circle over the bottom of the pie and flip the pie back over.

Slice into wedges and serve.