Pierce the eggs, put them in boiling water and cook for 8 minutes, then quench and peel. Peel the onion and cut into fine rings. Quarter and core the tomatoes and cut into small cubes without stems. Cut the corned beef into ½ cm cubes.
Whisk vinegar, salt and mustard together, add oil and chives. Mix in the onion, meat and tomatoes, arrange the salad and garnish with the chopped or quartered eggs.