Preheat oven to 375F and line a 9x13 baking dish with parchment paper.
In a large mixing bowl, combine all the dry and wet ingredients for the cake. Scrape the sides as you go, then pour into the baking dish and set aside.
In a separate mixing bowl, stir together the dry crumb topping ingredients before slowly adding in the remaining melted butter. Gently toss the crumb ingredients together using your hands until it forms little crumb balls. Evenly sprinkle the crumb topping onto the cake mixture in the pan, and then pop it in the oven.
Bake for 45 minutes, rotate, and then bake another 10 minutes or until a toothpick comes out clean. Let it cool.