Combine all vinaigrette ingredients in a bowl. Season to taste with salt and pepper.
Arrange egg in rows overlapping slices slightly. Season with salt and pepper to taste.
Pour olive vinaigrette over eggs. Scatter reserved watercress on top.
Use arugula instead of watercress.
Chop 3 anchovy fillets with 1 tablespoon capers and add to vinaigrette.
Serve as salad.