Preheat oven to 350°F with a rack in the center of the oven. Grease a 9 inch deep dish pie plate or 8x11 baking dish. Set aside.
In a large bowl combine pears, apples, juice, granulated sugar, flour, cinnamon, and vanilla. Stir gently until completely combined. Dump the mixture (and any accumulated juices) into the prepared baking dish.
In a separate bowl, combine oats, flour, brown sugar, salt, and cinnamon. Add melted butter and stir until combined. using your fingers, crumble the mixture over the fruit occasionally pressing some of it together to form clumps.
Lightly spray a piece of foil with nonstick spray. Cover the fruit crisp and bake for 20 minutes. Remove the foil and bake for another 20-25 minutes, until the fruit juices are bubbling and the topping is golden. Place on a rack to cool for about 15 minutes. Serve warm with vanilla ice cream.
* I used about 1.5 pounds of pears (3 medium) and 1 pound of apples (2 large). I recommend Honeycrisp, Pink Lady, or Fuji apples for this recipe. Apples and pears should be sliced ¼ inch thick or thinner.