In a bowl or zip-top bag, combine grated onion and juice, olive oil, garlic, Aleppo pepper, summer savory, salt, and pepper.
Add steak and turn to coat. Cover and refrigerate at least 1 hour, up to overnight.
While the steak marinates, toss sliced red onion with a pinch of salt and a splash of lemon juice or vinegar; let sit 15-20 minutes, then drain.
Soak dried morels in 2 cups warm water for 20-30 minutes, until softened. Lift out (leaving sediment behind), rinse briefly, and pat very dry. Halve any large morels.
Whisk together tahini, pomegranate molasses, lemon juice, and garlic. Add water gradually until smooth and pourable. Stir in olive oil and season with salt.
Remove steak from marinade, scraping off excess onion. Heat a skillet or grill pan over high heat.
Sear or grill steak 3-5 minutes per side for medium-rare, or until desired doneness. Remove and let rest 5-10 minutes, then slice thinly against the grain.
Melt butter in a skillet over medium-high heat. Fry morels 4-6 minutes, stirring occasionally, until golden and crisp at the edges. Add garlic during the last minute; season with salt.
Arrange lettuce on a platter. Top with cucumber, tomatoes, and pickled onion.
Layer sliced steak over the vegetables.
Scatter pomegranate arils, walnuts, fried morels, parsley, and mint over the top.
Finish with sumac and a generous drizzle of tahini-pomegranate dressing. Serve immediately.