Drain the corn and tuna well, then pick the tuna apart with a fork. Clean, wash, spin dry the lettuce and pluck it into bite-sized pieces. Clean, wash and slice the radishes. Rinse the chives well, shake dry and cut into rolls.
Mix the yogurt with the mustard. Season to taste with sugar, salt and pepper. Mix in half of the chives.
Arrange the lettuce, radishes, tuna and corn on 4 plates. Peel and quarter the eggs and add to the salad. Drizzle with the yoghurt dressing and sprinkle with the remaining chives.