Slow Cooker Apple Crisp

Mix flour, brown sugar, 1/2 cup of white sugar, 1/2 teaspoon cinnamon, nutmeg, and salt together in a bowl. Combine butter with the flour mixture using fingers or a fork until coarse crumbs form. Stir in walnuts and set aside. Whisk together 1/3 cup sugar, cornstarch, ginger, and 1/2 teaspoon cinnamon. Place the apples in a slow cooker, stir in the cornstarch mixture; toss with lemon juice. Sprinkle the walnut crumb topping on top. Cover and cook on High for 2 hours or Low for 4 hours, until apples are tender. Partially uncover the slow cooker to allow the topping to harden, about 1 hour.