Preheat oven to 350ºF. Using a 15 x 10” jellyroll sheet pan, grease sides and bottom and line with parchment paper.
In a large bowl mix together all dry ingredients. In another bowl whisk the wet ingredients together. Add to dry mixture, stir well to combine. In another bowl mix all the crumble topping ingredients together.
Pour batter onto baking sheet, spread out evenly. Evenly sprinkle the top with the crumble mixture. Bake for 40 minutes or until edges start to become golden, do not over-bake. Allow to cool completely in the pan before removing, up to one hour. Once cool, remove from pan to a cutting board and cut into 24 bars. Does not require refrigeration. Best eaten within 3-5 days, or freeze extras up to one month.