Preheat oven to 350°F. Grease a 9 1/2 inch deep dish pie plate (or similar sized baking dish). Set aside.
In a large bowl combine pears, apples, orange juice, granulated sugar, flour, cinnamon and vanilla. Stir gently until completely combined. Dump the mixture (and any accumulated juices) into the prepared baking dish.
For the topping: 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. Bake for 45-60 minutes, until the fruit is tender (check it with a sharp knife), the top is golden brown and it is bubbling around the edges. Serve warm with vanilla ice cream.
Apples and pears should be sliced 1/4 inch or smaller.