Preheat oven to 350f degrees. Spray a 9x13-inch baking dish with nonstick cooking spray.
Make the crumble topping:
In a small bowl, combine flour, brown sugar and butter using a fork. You want to end up with it fully mixed and you should have small crumbles.
Then, stir in chopped pecans. Set aside.
Prepare the cake:
First, open up the can of crushed pineapple and set aside 4 teaspoons of pineapple juice to use for the icing later.
In a large bowl, combine the crushed pineapple (with the rest of the juice), lemon cake mix, eggs and oil. Mix for about 2 minutes using an electric mixer.
Pour cake batter into prepared baking dish. Sprinkle crumb mixture evenly over the top of the cake batter.
Bake for about 35-38 minutes (until it bounces back to the touch or an inserted toothpick comes out clean.) Allow the cake to cool completely.
Making the icing:
In a small bowl, whisk together the powdered sugar, milk and pineapple juice. Whisk until smooth.
Drizzle the icing all over the cake. Slice and serve.
Video
Notes
Pineapple cake mix can be used instead of lemon. I just preferred the bright flavor that lemon added.