Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2). For the lime sauce, peel and finely dice the onion. Peel 1 lime thick enough to remove the white skin. Chop the flesh finely.
Squeeze the remaining lime. Mix 50 ml olive oil and lime juice. Stir in onion, lime pieces and capers. Season with salt and pepper.
Peel and wash the potatoes and cook them in boiling salted water for 12-15 minutes. Rinse fish pieces cold, dab dry and salt. Place in an ovenproof dish. Add lime sauce and bake in a hot oven for about 14 minutes.
In the meantime, drain the potatoes, let them drain and cut them in half. Heat 2 tablespoons of oil in a large pan and fry the potato halves until golden brown, turning them over. Season with salt and pepper.
Sort the spinach, clean and wash it thoroughly. Roast sesame seeds in a pan without fat until golden brown. Remove. Heat 1 tbsp. oil in a frying pan. Let the spinach collapse in it. Mix with mayonnaise and sesame seeds.
Season vigorously with sesame oil, salt, pepper and paprika. Serve.