Preheat oven to 350 and grease a 9 x13 inch baking dish with cooking spray.
Prepare the cake. Combine cake mix, egg, greek yogurt, melted butter, and vanilla and mix until combined. It's okay if the batter still has some lumps.
To make the crumble. Whisk together flour, brown sugar, sugar, salt, and cinnamon. Cut in chilled butter until crumbly. Set aside.
Spoon half the cake batter in the bottom of the greased baking dish. Take half of the crumble mixture and evenly sprinkle over the first layer of batter. Grease a rubber spatula and gently spread the remaining batter over the crumble (see note). Top with remaining crumble.
This takes a little finessing but it's worth it if you just work with it. If you don't want to worry about working with the batter (which is thick) to make the layers, you can spread all of the batter in the pan, then top with all of the crumble and bake as directed.