Preheat a grill to high.
For the creamy goat cheese dressing: In a medium mixing bowl, combine the goat cheese, mayonnaise, sour cream, chives, lemon zest and juice, honey, vinegar, salt and pepper. Whisk together well to break up the goat cheese. Cover and refrigerate for 30 minutes prior to serving.
For the salad: In a large mixing bowl, gently combine the cauliflower, carrots, bell peppers, onion, olive oil, red pepper flakes, salt and pepper. Char the vegetables on the grill on all sides, 6 to 8 minutes, removing the vegetables to a baking tray as done. Let cool. Cut the vegetables into a 1/2-inch dice.
In a large mixing bowl, combined the charred vegetables and celery root. Pour the creamy goat cheese dressing over the top and mix together well. Put the arugula on a platter and top with the salad. Garnish with the crumbled goat cheese. Serve immediately.