Scrub the potatoes and put them in a small roasting tin. Prick with a fork, drizzle with the oil and sprinkle with a little salt. Place in a preheated oven, 200°C (400°F), Gas Mark 6, for 45 minutes until tender.
Make the salsa, meanwhile. Finely chop the tomatoes and mix with the onion, celery, coriander, lime juice and sugar in a bowl.
Halve the potatoes and fluff up the flesh with a fork. Sprinkle with the cheese and top with the salsa. Serve with a green salad.