In a large salad bowl toss together well the romaine, the Boston lettuce, the curly endive, and the watercress. In a skillet cook the bacon over moderate heat, stirring, until it is crisp and transfer it with a slotted spoon to paper towels to drain. Halve, pit, and peel the avocados and cut them into 1/2-inch pieces. Arrange the chicken, the bacon, the tomato, and the avocado decoratively over the greens and garnish the salad with the grated egg and the chives. In a small bowl whisk together the vinegar, the mustard, and salt and pepper to taste, add the oil in a slow stream, whisking, and whisk the dressing until it is emulsified. Stir in the Roquefort. Whisk the dressing, pour it over the salad, and toss the salad well.