Whisk together the mayonnaise, mustard, lemon juice, garlic, hot sauce, 1/4 teaspoon of salt, green onions, capers, shallots, parsley and egg in a medium bowl. Gently fold in the crabmeat, turning to gently coat with the dressing and being careful not to break up the lumps. Adjust seasonings, to taste. Refrigerate for 30 minutes before serving.
In a large bowl, combine the red and yellow tomatoes, watercress, and 3 tablespoons of the chives. Season with salt and pepper. Drizzle the olive oil over the salad and toss to coat well.
Arrange the tomato and watercress mixture on each of 8 salad plates. Divide the crabmeat mixture evenly among the tops of the salads. Garnish the salads with the remaining tablespoon of chopped chives and serve immediately.