Heat 1/2 the oil in a large frying pan over medium heat. Add onion. Cook, stirring occasionally, for 5 minutes or until softened. Add garlic, fennel and cumin. Cook for 1 minute or until fragrant. Transfer to the bowl of a 5.5-litre slow cooker. Reserve 1 tablespoon cider. Add remaining cider to slow cooker with sugar and stock. Stir to combine.
Heat remaining oil in pan over medium-high heat. Add pork. Cook, turning, for 5 minutes or until browned. Transfer to slow cooker. Cover with lid. Cook on low for 6 to 8 hours (or on high for 4 hours)
Using 2 forks, roughly shred pork. Combine aioli, lemon juice and reserved cider in large bowl. Add apple, walnuts, green onion and dill. Season well with salt and pepper. Toss to combine.
Place 1/2 the bread slices on a flat surface.Top with pork and apple slaw. Sandwich with remaining bread slices. Serve.