Preheat the grill to medium-high. Prepare the iceberg wedges by shaving off most of the core with a knife while keeping the base intact. Brush each one with olive oil, and season with salt and pepper. Place them on the grill and cook for 12 to 15 minutes, rotating as needed to promote even charring. Remove from grill and transfer to serving dishes.
While the wedges are cooking, whisk together the yogurt, blue cheese, apple cider vinegar, garlic powder, and water to your desired consistency.
Assemble the salads by topping each grilled wedge with cherry tomatoes, chives, and blue cheese. Drizzle with the dressing. Serve warm.
Make the dressing up to 5 days in advance. Store in the fridge, and stir well before using.
Serve this salad with grilled fish, burgers, or tofu. You can also add white beans to the salad to bulk it up. It's best served right away, but leftovers can last in the fridge for a couple of days.
If you don't have apple cider vinegar for the dressing, use white vinegar or lemon juice.