In a medium mixing bowl, whisk together the chickpea flour, warm water, salt, and 2 tablespoons of the olive oil until smooth and lump-free.

Let the batter rest at room temperature for at least 15 minutes to allow the flour to hydrate fully, which ensures a better texture.

While the batter rests, preheat your oven to 450°F (230°C) and place a 10-inch cast-iron skillet or round baking pan inside to heat up.

Carefully remove the hot skillet from the oven and swirl the remaining 2 tablespoons of olive oil to coat the bottom and sides evenly.

Pour the chickpea batter into the hot skillet; you should hear a slight sizzle as the batter hits the oil.

Immediately scatter the thinly sliced red onion and chopped fresh rosemary evenly over the top of the batter.

Sprinkle the freshly ground black pepper over the toppings for an extra kick of spice.

Bake in the preheated oven for 20 to 25 minutes, or until the edges are golden brown and pull away from the sides of the pan.

Turn on the broiler for the last 2 minutes to get the onions nicely charred and the top extra crispy.

Remove from the oven, let it cool for 5 minutes to set, then slice into wedges and serve warm.