Preheat the oven to 350 degrees F. Butter the inside of a 10 by 15 by 2 1/2-inch oval baking dish.

Immerse the peaches in boiling water for 30 seconds, then place them in cold water. Peel the peaches and slice them into thick wedges and place them into a large bowl. Add the orange zest, 1/4 cup granulated sugar, 1/2 cup brown sugar, and 2 tablespoons of flour. Toss well. Gently mix in the raspberries. Allow the mixture to sit for 5 minutes. If there is a lot of liquid, add 1 more tablespoon of flour. Pour the peaches into the baking dish and gently smooth the top.

Combine 1 1/2 cups flour, 1 cup granulated sugar, 1/2 cup brown sugar, salt, oatmeal, and the cold, diced butter in the bowl of an electric mixer fitted with a paddle attachment. Mix on low speed until the butter is pea-sized and the mixture is crumbly. Sprinkle evenly on top of the peaches and raspberries. Bake for 1 hour, until the top is browned and crisp and the juices are bubbly. Serve immediately, or store in the refrigerator and reheat in a preheated 350 degree F oven for 20 to 30 minutes, until warm.