In a large mixing bowl, stir together the ingredients for the crumb topping; Flour, brown sugar, white sugar, cinnamon, nutmeg, and salt. Combine butter with this mixture using a pastry blender or a fork until coarse crumbs form; set aside.
In a small bowl, stir together white sugar, cornstarch, ginger, and cinnamon. Place sliced apples in the slow cooker, stir in the cornstarch mixture, and toss with lemon juice.
Sprinkle the crumb topping over top.
Cover and cook on high 2 hours or on low 4 hours, or until apples are tender.
Partially uncover the slow cooker and cook for an additional hour allowing the topping to harden.