Remove bones and skin from salmon; break into chunks. In a medium bowl, mix yogurt, hot-smoked salmon, chopped onion, chives, mustard, and pepper with a fork until well combined. Gently stir in salmon, season to taste with salt, and top with slivered onion. Serve with lavash.
Make ahead: Chill, covered, up to 3 days (you may need to moisten with a bit more yogurt).
Note: Nutritional analysis is per 1 1/2-tbsp. serving.