Turn broiler on in oven. Place a cast iron or broiler safe skillet on rack 6 inches below broiler. Let it heat while you prepare ingredients.
In a large mixing bowl, combine flour, water, 2 tbs olive oil, salt, rosemary, and garlic. Whisk together vigorously. Let it sit for 5 minutes (while your skillet is heating).
Finely chop your onion, set aside.
Remove your heated skillet from the oven, toss in your chopped onion, return to broiler and let cook for 1 minute.
Remove your skillet, drizzle with 1 tsp of olive oil. Pour your farinata (socca) batter into hot skillet and tilt to evenly coat bottom. Drizzle remaining 1 tsp olive oil on top.
Place skillet under broiler and cook your chickpea flour pizza crust for 5-7 minutes, or until edges are browning and top is blistered.
Remove your crust from oven. Top with Mezzetta’s Marinara. Sprinkle with crumbled feta cheese (or toppings of your choice).
Return to broiler and cook for 5 minutes, or until toppings are warm/beginning to brown.
Remove from oven, let cool a few minutes, slice & serve.