Combine scallions, lemon zest, and juice in a large bowl. Season with salt and pepper and let sit for at least 5 minutes or up to 1 hour.
Step 2
Stir in labneh (start with ½ cup and add more to taste after the following ingredients), then fold in picked fish, sliced celery, parsley, all but 1 tablespoon dill, and sliced chives. Season with more salt, pepper, and lemon juice to taste.
Step 3
Top with reserved dill and celery leaves. Serve with toast, bagels, or crackers, as well as lettuce, cucumbers, and lemon.