Preheat oven to 350 degrees F. Grease a 9x13 inch baking dish.
Prepare the fruit base: In a large mixing bowl, combine apple, pears and lemon juice; toss to coat. In a medium bowl mix granulated sugar, brown sugar, flour and apple pie spice. Sprinkle sugar mixture over apples and pears tossing to coat. Pour apple pear mixture into prepared pan, spread into an even layer.
Prepare the topping: In a large bowl, combine the oats, flour, apple pie spice, salt, pecans and brown sugar. Mix butter and vanilla together and pour over oat mixture; stir to combine. Crumble mixture evenly over the apples and pears.
Bake in preheated oven for 40-45 minutes or until the crumble topping is golden brown.
Serve warm. If desired, top with vanilla ice cream, caramel sauce, or whipped cream.
Notes
I used Honeycrisp apples. If you are using very tart Granny Smith apples, you may want to add an additional 2 tablespoons of granulated sugar to the fruit filling.