Step 1Combine the flour and salt in a medium bowl. Whisk in the water and 1 tablespoon olive oil until smooth. Cover the batter loosely and let stand at room temperature, preferably for 4 to 8 hours.
Step 2Heat 1 tablespoon oil in a well-seasoned 10-inch cast iron skillet over medium heat. Add the onion and sauté until golden brown and tender, about 15 minutes. Reduce heat to medium low and continue to sauté until the onion is very brown and caramelized, about 8 minutes.
Step 3Using tongs, transfer the onion to a plate. Inspect the skillet to be sure that there are no spots where the onions stuck. Clean the skillet if necessary. (The onions can be cooked up to 8 hours ahead. Cover and keep at cool room temperature.)
Step 4Heat the oven to 450 degrees. Place the skillet in the oven and heat until very hot, about 15 minutes. Working quickly, pour the remaining 1 tablespoon olive oil into the skillet and carefully swirl to evenly coat the bottom of the skillet. Whisk the batter and pour it into the skillet. Scatter the onions over the surface of the batter and sprinkle with cumin seed and Aleppo or black pepper. Bake until golden brown and set, about 15 minutes.
Step 1While the pancake is baking, prepare the salad: Whisk the olive oil, lemon juice and harissa as desired in a large bowl. Season to taste. Add the greens and feta and toss to coat with the dressing.
Step 2Cut the pancake into wedges and serve immediately with salad.