1. FOR THE VINAIGRETTE: Whisk all vinaigrette ingredients in medium bowl until well combined (alternatively, shake vigorously in tight-lidded jar); set aside. (Dressing may be refrigerated in airtight container for 1 day; bring to room temperature and shake well before using.)
2. FOR THE EGGS: Place eggs in medium saucepan, cover with 1 inch water, and bring to boil over high heat. Remove pan from heat, cover, and let stand 10 minutes. Meanwhile, fill medium bowl with 1 to 2 quarts ice water. Transfer cooked eggs to ice water with slotted spoon; let stand 5 minutes, then peel, cut into 1/2-inch cubes, and set aside.
3. FOR THE CHICKEN: Meanwhile, season chicken with salt and pepper. Adjust oven rack to 6 inches from broiler element; heat broiler. Spray broiler-pan top with vegetable cooking spray; place chicken breasts on top and broil chicken until lightly browned, 4 to 8 minutes. Using tongs, flip chicken over and continue to broil until thickest part is no longer pink when cut into and registers about 160 degrees F on instant-read thermometer, 6 to 8 minutes. When cool enough to handle, cut chicken into 1/2-inch cubes and set aside.
4. TO FINISH THE SALAD: Toss romaine and watercress with 5 tablespoons vinaigrette in large bowl until coated; arrange on very large, flat serving platter. Place chicken in now-empty bowl, add 1/4 cup vinaigrette and toss to coat; arrange in row along one edge of greens. Place tomatoes in now-empty bowl, add 1 tablespoon vinaigrette and toss gently to combine; arrange on opposite edge of greens. Arrange reserved eggs and avocados in separate rows near center of greens and drizzle with remaining vinaigrette. Sprinkle bacon, cheese, and chives evenly over salad and serve immediately.

Yield: 8 servings