Cut salmon in small pieces, about 1/4-inch thick. Set aside or cover and refrigerate until ready to serve. Slice cucumber into very thin (almost transparent) rounds and set aside. In a medium bowl, mix together the shallots, dill, chives, capers
, lemon juice
and finally add the salmon. Cover and refrigerate if not using immediately. Just before serving, chop
the tomatoes, season with salt and pepper and a sprinkling of olive oil, and stir to combine. On a serving plate, spread the cucumber slices to cover 2/3 of the plate, leaving a space in the center of the plate. Then arrange the salmon over the cucumber, then top with the seasoned tomatoes. Garnish with sliced avocado
and chopped chives
. Serve with endive, toast points or crackers.