Peel, core, and chop each apple into 1’2” pieces.
Place all the apple pieces in the bowl of the slow cooker. Pour orange juice and vanilla over the apples and stir to combine.
In a mixing bowl, combine oats, flour, brown sugar, baking powder, and cinnamon. Using a fork stir well to combine all the dry ingredients.
Add melted butter and using a fork mix well until you get a crumble consistency. Since we are using less butter than a usual crumble, the mixture will not be very wet. Sprinkle over apples in slow cooker.
Cover and cook on high for 4 hours until apples are soft. You can also reduce the heat to low after 3 hours and keep it slow cooking for up to six hours so it stays warm for your after-dinner dessert.
Serve with frozen vanilla yogurt.