Preheat oven to 350F.
Peel, core and cut the pears and apples into large chunks. Place the fruit in a large bowl and add the zests, juices, flour, cinnamon, and nutmeg, Pour into an 9 x 12 x 2-inch oval baking dish.
For the topping, combine all the ingredients in the bowl of an electric mixer fitted with the paddle attachment. Mix on low speed for 1 minute, unit the mixture is large crumbles. Sprinkle evenly over the fruit, covering the fruit completely.
Place the baking dish on a sheet pan and bake for 50 minutes to 1 hour, until the top is brown and the fruit is bubbly. Serve warm.