Start by making the apple filling. Add the apple slices, lemon juice, vanilla, brown sugar, cinnamon, nutmeg, salt, and flour to the bowl of your slow cooker. Toss all the ingredients together well then spread them into an even, flat layer.
6 apples, 1 lemon, juiced, 1 tablespoon vanilla extract, ½ cup brown sugar, 1 tablespoon ground cinnamon, ¼ teaspoon ground nutmeg, ¼ teaspoon salt, ¼ teaspoon flour
Mix all of the ingredients for the oat topping together in a separate mixing bowl. Sprinkle the oat mix over the apples inside the slow cooker.
1 ¼ cup rolled oats, ½ cup flour, ⅓ cup brown sugar, 1 teaspoon ground cinnamon, ¼ teaspoon salt, 4 tablespoons butter, melted
Place a dish towel or paper towel across the top of the slow cooker then put the top on, over the towels. The towels will absorb some of the steam from the apples as they cook and prevent the crisp topping from getting soggy.
Set the slow cooker to low and cook for 7-8 hours. When the crisp is ready, the apple filling will be bubbling around the edges.
Scoop the crisp right out of the slow cooker and enjoy while warm!