How to Make It
In a medium saucepan, cover the potatoes with water, add a large pinch of salt and bring to a boil. Cook over moderate heat until tender, 25 to 30 minutes. Drain the potatoes and let cool slightly, then peel and cut them into 1/2-inch dice.
Meanwhile, in a small saucepan, cover the egg with water and bring to a boil. Simmer over moderate heat for 10 minutes. Drain and cool under running water, then peel and coarsely chop the egg.
In a medium bowl, toss the potatoes with the egg, spinach, celery, onion, vinegar, za’atar and the 1/3 cup of olive oil. Season the potato salad with salt.
Light a grill or preheat a grill pan. In a small bowl, combine the Aleppo pepper and fenugreek. Brush the fish with olive oil, sprinkle on both sides with the spice mixture and season with salt. Grill the fish skin side down over high heat until the skin is crisp, 3 to 4 minutes. Turn the fish and cook just until white throughout, about 1 minute longer. Transfer the branzino to plates and serve with the potato and spinach salad.
Za’atar is a Middle Eastern blend of sesame seeds, herbs and sumac. Aleppo pepper is a moderately hot crushed dried chile from Syria and Turkey. Both are available at Middle Eastern markets and penzeys.com.