Preheat oven to 350 degrees F
Place the apples and pears in a large bowl and toss with the lemon juice, crystalized ginger and cinnamon until everything is evenly incorporated. Transfer to mixture to a baking dish big enough to hold all the fruit.
In another bowl, combine the butter, sugar, oats and flour and using a pastry cutter, or a fork, cut the butter into the ingredients until you have a course crumbly mixture.
Pour the crumble mixture on top of the fruit and evenly distribute everything so the fruit is covered.
Place the baking dish into the oven and bake for 45-50 minutes until the top is golden brown.
Remove the baking dish from the oven and let rest for 5 minutes.
Serve with vanilla ice cream if desired.