Scrub the potatoes and put them in a small roasting tin. Prick with a fork and sprinkle with a little salt. Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 45 minutes until tender. (If you do not have the time to bake the sweet potatoes, they can be microwaved like ordinary ones, although this way you will lose the wonderful crispy baked flavour. Prick them with a fork and cook on the highest setting for 15–20 minutes, or according to the manufacturer's instructions.)
Meanwhile, make the salsa. Mix the tomatoes in a bowl with the onion, celery, coriander, lime juice and sugar.
Halve the potatoes and fluff up the flesh with a fork. Sprinkle with the cheese and serve topped with the salsa.