1. Preheat oven to 350 degrees Fahrenheit.
2. In a large bowl, stir together pears, apples, lemon juice, vanilla, brown sugar, cinnamon, and cornstarch until combined.
3. Pour mixture into a greased 9x9-inch baking dish.
4. In the same bowl, stir together oats, brown sugar, and salt. Add butter cubes and use a pastry blender or two butter knives to cut butter into the dry mixture, until coarse crumbs form.
5. Sprinkle oat topping over the fruit. Bake for 35-40 minutes.