Wash the potatoes and possibly halve them. Cover and cook in boiling salted water with broth for about 20 minutes.
In the meantime, wash the fish and pat dry. Marinate with lemon juice, season with salt. Clean and wash the cucumber, quarter it lengthwise and cut it into pieces. Wash and halve the tomatoes. Mix 2 tablespoons pesto, salad cream, vinegar and 1 teaspoon sugar.
Heat the oil in a large frying pan. Fry the fish for 2-3 minutes on each side.
Drain the potatoes and collect approx. 6 tbsp. of cooking liquid. Mix with the pesto cream and mix with the potatoes and vegetables. Season to taste with salt and pepper. Arrange potato salad and fish, sprinkle with remaining pesto.
Garnish with basil if desired.