Cut a thin slice from stem-end of each tomato; scoop pulp and seeds from center with a small, sharp-edged spoon.
Or make a deep X-cut from top of tomato almost to bottom; carefully pull tomato open at top and scoop out pulp and seeds.
Turn tomatoes cut-side down on paper towels to drain.
Chop salmon very fine.
In a medium bowl, stir cream cheese until smooth.
Stir in chopped salmon, lemon juice and 1 tablespoon minced watercress.
Sprinkle inside of drained cherry tomatoes with salt and pepper to taste.
Fill each with salmon mixture; top each with a small sprig of watercress.