Preheat oven to 350°F. Spray a 9x5-inch or 8x4-inch 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.
Pour batter into prepared pan. Combine cinnamon and sugar for topping; sprinkle over bread.
Bake for 40-50 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.
Cool before removing from pan. Store in an airtight container for up to 2 days or freeze for up to one month.
To make your own buttermilk, add 1/2 teaspoon of vinegar or lemon juice to a measuring cup and fill with milk to 1/3 cups. Let sit for 5 minutes.