Preheat oven to 180°C. Halve sweet potatoes lengthways. Prick flesh with a fork, place on a baking tray, cover with foil and bake for 30 mins or until tender.
Meanwhile, heat oil in a saucepan over medium heat. Add onion, celery and carrot and cook for 8 mins or until softened. Add tomatoes, sauce, mustard and chilli, if using, and half cup water. Simmer for 5 mins. Stir in beans and 150g ham, and cook for 10 mins or until mixture thickens.
Scoop flesh from potatoes, leaving a 1cm-thick shell. Place flesh into a bowl and mash with a fork then season.
Fill potato shells with bean mixture and top with remaining ham and cheese. Bake for 10 mins or until cheese is melted and golden. Top with mashed potato and extra sauce, and serve with rocket.