Preheat oven to 375 degrees F. Mix together topping ingredients in a small bowl. It should be a crumbly mixture.
For batter, Mix together your dry ingredients (including the zest) and then add in your egg, followed by milk and OJ. Finally, stir in melted butter.
In an 8×8 baking dish (lightly buttered) you want to pour in about half of your batter, followed by half of your topping, followed by the rest of your batter and then the rest of your topping.
Bake this for about 30-35 minutes at 375. A toothpick should come out cleanly from the center.
Let this cool for at least 5 minutes before chopping into it.