Boil the egg hard for about 10 minutes. Sort watercress and wash thoroughly. Cut into small pieces if necessary. Peel and wash the asparagus. Peel the asparagus lengthwise in strips with an asparagus peeler. Wash, clean, quarter and seed the tomato. Cut the flesh into small cubes.
Wash the chives, dab dry and cut into small rolls. Quench egg cold, peel and cut into cubes. Mix oil and vinegar. Stir in egg, tomato and chives. Season with salt and pepper. Arrange the watercress and asparagus slicer with the egg and tomato vinaigrette on two plates