Wash the potatoes thoroughly, grate them dry and wrap them in aluminium foil. Cook in the preheated oven (electric cooker: 200 °C/ circulating air: 175 °C/ gas: see manufacturer) for approx. 2 hours.
Boil 125 ml of water. Put the couscous in a bowl. Add 1 tablespoon of oil, salt and water and stir well. Set aside and allow to soak.
Peel and finely grate the carrot. Wash, drain and quarter the tomatoes. Peel the cucumber, quarter it lengthwise and remove the seeds. Cut cucumber into small pieces. Clean, wash and drain spring onions and cut into rings. Add carrot, tomatoes, cucumber, spring onions, 1 tbsp. oil and lemon juice to the couscous, mix well, season with salt and pepper.
Sort the spinach, wash and blanch in boiling salted water for about 2 minutes. Rinse in cold water, pour into a sieve and drain well. Cut the spinach into small pieces. Mix yoghurt, chili flakes and spinach, season with salt and pepper.
Take potatoes out of the oven, open aluminium foil. Cut potatoes lengthwise and press them together. With a small fork, crush the inside into coarse pieces. Put 2 tablespoons of cheese and 1 teaspoon of butter in each potato and let it melt a little. Crush the inside to a pulp with a fork. Put the couscous salad on the potatoes and serve with spinach sauce.