In a medium bowl, whisk together the sour cream, mayonnaise, sweetener, lemon juice, and fresh chives until smooth and well combined. The sweetener balances the richness of the mayo and sour cream, while the lemon juice adds brightness. Set the dressing aside at room temperature—you'll drizzle it over the salad just before serving to keep the lettuce crisp.

In a large serving dish or shallow bowl, create distinct horizontal layers in this order: start with the chopped iceberg lettuce as your base, then layer the halved cherry tomatoes, followed by the diced red onions, then the chicken breast cubes, and finally the crumbled bacon. Keep each ingredient in its own section rather than mixing—this is what makes a Cobb salad visually appealing and allows diners to enjoy each component. I like to arrange the layers slightly offset so you can see all the colors when looking at the salad from above.

Arrange the hard-boiled egg slices on top of the layered salad, then sprinkle the diced avocado and shredded cheddar cheese over everything as the final garnish. Cover the dish loosely with plastic wrap and refrigerate for at least 2 hours (or up to 4 hours)—this chilling time allows the flavors to meld slightly while keeping all the components cool and fresh. I've found that chilling helps the cheese flavor come through better and gives the salad a more cohesive taste when served.

Remove the salad from the refrigerator and drizzle the prepared dressing from Step 1 evenly over the top just before serving. You can serve the dressing on the side instead if you prefer—this way, guests can add as much or as little as they like, and the salad won't become soggy. Toss gently at the table if desired, or let guests serve themselves and mix their own portions.