Spray slow cooker generously with non-stick cooking spray.
Toss together the chopped pears and blueberries in the base of the slow cooker and sprinkle with a little lemon juice. Add the cinnamon, ginger and (if you have it on hand) a pinchful of cardamom.
In a small mixing bowl, combine the oats, flour, sugar. Cut in the butter using a pastry blender or two knives.
Spread the topping evenly over the blueberries and pears in the base of the slow cooker.
Set on low and cook for 4 hours.
Serve Pear Blueberry Crumble as is, or with ice cream or whipped cream.