Preheat oven to 350°F. Spray a 9x5” loaf pan with cooking spray.
Stir granulated sugar and brown sugar with oil and pumpkin. Stir in the eggs, pumpkin pie spice, salt, and baking soda. Stir until combined. Stir in buttermilk and flour just until combined. Fold in 1 cup of the chopped peanut butter cups.
Pour batter into prepared pan. Sprinkle the remaining peanut butter cup chunks over the top of the bread. Bake for 40-45 minutes. If you want it totally done (no gooey center), test it by inserting a toothpick just partway into the top center of the bread. If this comes out clean, it’s done. If you like a gooier center, remove it when testing it with at toothpick that way comes out with a little stuck to the top.
Let the bread cool before cutting. Store in an airtight container for up to 3 days or slice and freeze in individual sandwich bags.