1. Preheat oven to 350 degrees F. Grease and flour a 9" x 13" pan.
2. Topping: Mix together sugars and flour. Using fingers, mix in melted butter so it resembles wet sand.
3. Mix all dry cake ingredients in a large bowl. In a separate bowl whisk together yogurt, sugars, eggs and butter. Fold into flour mixture and add chopped apricots and orange zest. Mix until combined then pour into prepared pan and smooth the top. Sprinkle streusel topping evenly over top.
4. Bake for 45-50 minutes, rotating pan halfway through baking time. Toothpick inserted in centre should come out with just a few crumbs attached.