Cut the smoked or pickled salmon into fine cubes. Halve and squeeze the lime. Dice the avocado and immediately sprinkle with 1 tbsp of lime juice to prevent it from discoloring. Wash the dill, pat dry and pluck off the leaves. Clean the spring onion and cut into fine rings. Clean the hearts of romaine lettuce, divide into individual leaves, wash and spin dry. Mix together the rest of the lime juice, mustard seeds, olive oil and salt. Fold the salmon, avocado, dill and spring onion into the sauce, leave to infuse for 10 minutes. Arrange the romaine lettuce leaves on 2 plates and fill with the avocado and salmon mixture.