Prepare the dressing: In a small bowl or jar, whisk together the mayonnaise, sour cream, Dijon mustard, extra virgin olive oil, minced garlic, and lemon juice until smooth and creamy.
Season with salt and pepper to taste.
Combine the salad : In a large bowl, combine the cooked chicken, crumbled bacon, chopped eggs, cherry tomatoes, red onion, and celery.
Dress the salad: Pour about three-quarters of the dressing over the salad and toss gently to coat everything evenly.
Add avocado and serve: Gently fold in the cubed avocado.
Taste and add more dressing if desired.
Serve immediately over a bed of fresh lettuce.