Char the romanesco. Heat a large skillet over medium-high heat. In a large mixing bowl, toss the romanesco with a drizzle of neutral oil and season with salt. Add to the skillet and cook for 5 minutes, or until well-charred on one side. Give the pan a shake and continue cooking until the romanesco is cooked through but still has a bit of bite.
Make the dressing. While the romanesco cooks, make the dressing (you can use the same bowl you used to toss the romanesco). Add the red onion, lemon, olive oil, sumac, a pinch of salt, and several cracks of black pepper. Whisk together.
Toss and season the salad. When the romanesco is done, transfer it back into the bowl along with the chickpeas, olives, feta, and herbs. Toss everything together and taste for seasoning. Go easy with the salt at first because the olives and feta will provide quite a bit. Allow the salad to sit for 5-10 minutes for veggies to absorb some dressing and the flavors to mingle. Toss and taste for seasoning again. If the salad seems dry, add a bit more olive oil. If it needs more punch, add a splash of red wine vinegar.
Serve. Spoon into large bowls and top with a sprinkle of sumac. Serve with crusty bread or as a side for a mezze spread.