Preheat oven to 375 degrees.

In a large bowl, combine all the fruit topping ingredients and stir to distribute the dry ingredients and zest evenly through the fruit.

In a medium bowl, combine the flour and brown sugar, breaking up any lumps with a fork. Using your fingers or a pastry cutter, work the butter into the flour and sugar until the mixture resembles coarse meal.

Lightly butter a 9 x 13 inch baking dish and spoon the fruit filling into it. Distribute the streusel topping evenly over the top of the fruit.

Put the crisp in the oven and bake it for about 1 hour, checking it halfway through baking. You'll probably see yummy bubbling fruit juices around the edges long before it's done, but keep on baking the crisp. At the halfway point, you'll see that the streusel topping will look pretty pale. That's a sign it's not done yet.

By the end of the baking time, you'll want to check and make sure that the fruit juices are bubbling not just around the edges, but in the center, too. Make a small cut with a knife in the center to check for this. By this time, the streusel topping will have taken on a nice golden color, too.

Take the crisp out of the oven and cool on a rack until it's room temperature. Don't serve it when it's hot, or it will be too runny. Allow enough time for the crisp to cool fully. Serve it at room temperature, or slightly warmed-back-up in a low oven.