Cook the eggs: place in hot water, bring to a boil and cook for 5 minutes. Drain, run cold water over them and peel.
Rinse and dry the lettuce and arugula, place in a salad bowl. Add sliced radishes and peeled cucumber and chili slices. Season with salt and pepper (if the salad will sit on the table, season just before serving), mix gently.
Add the chopped eggs (into thick slices or halves) and feta cut into cubes.
Prepare the dressing: mix all dressing ingredients in a bowl (to ensure the feta dissolves well in the dressing and there are no lumps, you can first mash it with a spoon with honey, then mix with the remaining ingredients).
Drizzle with dressing, sprinkle with chives and watercress and serve.