Preheat oven to 350 F.
Use a food processor to puree the pie filling for the cake and the frosting. Set aside.
In a medium bowl, whisk to combine the flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl or the bowl of an electric mixer, beat together the oil, melted butter and sugar.
Beat in the sour cream followed by the vanilla. With the mixer running, add one egg at a time.
Add the dry ingredients alternatively with the milk.
Pour the batter into the cooled graham cracker crust. Smooth the batter with an offset spatula.
Evenly drop heaping teaspoonfuls of the pureed pie filling. Drag a toothpick or the tip of a knife through the pie filling. Be careful not to over-swirl or you won’t get the marbled look.
Bake 30-35 minutes until a toothpick comes out clean when inserted in the center of the cake. Remove cake from oven and place the pan on a cooling rack. Allow to cool completely.
Once cooled, pipe or spread the frosting on the cake. Serve slices with extra pie filling on top, if desired!