Place the fish in a dish. Mix together all the spice rub ingredients in a bowl and rub into the fish. Cover and marinate in the refrigerator for 30 minutes.
Mix all the cumin potato ingredients together and put on a baking sheet. Place in a preheated oven, 200°C (400°F), Gas Mark 6, for about 40 minutes or until crisp and golden.
Heat a griddle or frying pan until hot and cook the fish for 2 minutes on each side until crisp and golden. Serve with the potatoes and a mixed salad.