Halve the avocado and remove the stone. Lift the pulp out of the skin, cut a few thin slices to garnish and put aside. Coarsely chop the rest and immediately drizzle with a little lime juice. Mix these avocado pieces with cream cheese and mash with a fork. Add the mustard and the finely chopped shallot. Peel and dice the eggs and fold into the avocado mixture. Season the spread with salt, pepper, paprika powder and lime juice.
Spread the avocado and egg mixture on bread or rolls. Rinse the watercress and shake dry. Pluck the leaves from the stalks and place on the coated bread with the avocado slices.