Boil eggs hard and peel them. Wash fennel, cut off the stalk and remove the outer leaves. The inner parts half lengthwise and cook in salted water until al dente. Strain, refresh with cold water and let them drain on kitchen paper.
Cut eggs into very small cubes, wash and chop the light parts from the spring onions.
Stir well olive oil, vinegar, salt, pepper and spring onion in a bowl, add the eggs and mix well.
Serve fennel bulbs with egg vinaigrette.