In a medium bowl, whisk together the yogurt, olive oil, red wine vinegar, and Dijon mustard until smooth and well combined. Add the finely crumbled blue cheese and whisk until mostly incorporated—a few small cheese pieces can remain for texture. Stir in the fresh chives, kosher salt, and freshly ground black pepper. Taste and adjust seasoning if needed. Set the dressing aside at room temperature while you prepare the salad components. I prefer to make the dressing first so the flavors can meld slightly before serving.
Toss the chilled, chopped salad greens onto a large platter or individual plates, creating an even base. Arrange the grilled chicken breast slices, crispy bacon pieces, hard-boiled egg quarters, and halved cherry tomatoes in organized rows or sections across the greens. Just before serving, toss the avocado slices with the lemon juice to prevent browning, then add them to the salad. Sprinkle the crumbled blue cheese over the top.
Pour the blue cheese yogurt dressing from Step 1 over the assembled salad just before serving. You can drizzle it evenly across the top or serve it on the side so guests can dress their own portions. Toss gently if desired, or let each person mix their salad to their preference. I like to serve the dressing on the side since the yogurt base doesn't keep salad greens quite as crisp as a traditional vinaigrette.