Mix the chickpea flour, water, cumin and salt together until smooth. Whisk in the olive oil. Let sit for 2 hours at room temperature or overnight in the refrigerator. (If refrigerating, allow to come to room temperature for 2 hours before cooking.)
Preheat the broiler to high. In a 9-inch cast-iron pan on top of the stove, heat a small layer of oil until smoking. Add socca batter until a thin pancake forms. Cook until the edges just start to brown, then run the pan under the broiler. Broil until the batter looks cooked and starts to blister slightly.
Flip the socca onto a cutting board. Sprinkle with sea salt and drizzle with olive oil. Repeat with the remaining batter. Serve with toppings and cut into wedges.