Place an oven rack as low as possible in your oven and place a pizza stone on that rack. Place another oven rack near the top of the oven (second rung from the top). Turn the oven on to 450°F. Set up two baking sheets with parchment paper.
Make the roasted onion cream. On one baking sheet, combine the chopped onion, garlic cloves, 1 teaspoon of oil, salt, and pepper, Toss to combine and arrange in a single layer. Slide the baking sheet into the oven (top rack) and roast until onions are charring a bit on the edges, about 15 minutes. Remove onions and let cool slightly.
In an upright blender, combine the roasted onions and garlic, remaining tablespoon of oil, cashews, nutritional yeast, lemon juice, water, and some salt and pepper. Blend on high until totally smooth and creamy. Adjust seasoning if necessary. Scrape roasted onion cream into a small bowl and set aside.
While onions are roasting, you can also have the cauliflower cooking. In a large bowl, whisk together the chickpea flour, water, salt, and pepper until smooth. It should have the consistency of thin pancake batter. Drop the small cauliflower florets into the batter and stir until all pieces are lightly coated. Using a slotted spoon, carefully transfer battered cauliflower to the baking sheets, tapping off excess batter before setting on the baking sheet. Spread cauliflower out as much as you can and slide into the oven. Bake for 20 minutes, or until batter is dry and slightly browned. Remove cauliflower from the oven and let cool slightly
Rinse out the large bowl that you used to batter the cauliflower. Pour the hot sauce and tablespoon of oil into the bowl and whisk to combine.
Transfer the battered and baked cauliflower to the bowl with the hot sauce, breaking up the pieces if necessary. If there are baked bits of batter, break them off and discard them. Toss the battered cauliflower in the hot sauce mixture until it is evenly coated. Return the sauced cauliflower to the baking sheet. Bake the cauliflower for another 15 minutes or until edges are slightly browned and exterior is dry. Remove cauliflower once sufficiently cooked and let it cool slightly. Increase the oven temperature to 500 degrees F.
Dust your working surface and a pizza peel with flour OR line it with a piece of parchment paper. Start stretching/rolling out the dough until you have a 12-inch circle of even thickness. Carefully transfer the dough circle to the floured/papered peel. If you use the paper method, trim the paper so that you have a ½ inch border around the circle of dough.
Spread the roasted onion cream on the pizza evenly, leaving about ½ an inch at the crust area. Top the pizza with all of the Buffalo battered cauliflower. Lightly press the battered florets into the onion cream and dough.
Jiggle the pizza peel to ensure that the pizza will come loose. If it’s sticking, carefully lift up the edges and toss in a bit more flour until it seems to loosen from the peel. If you’re using parchment, ignore this step!
Open the oven and with equal measures of care and efficiency, slide the pizza off of the peel and onto the hot stone with a few flicks of your wrist (or just pull a tab of the parchment paper). Close the oven immediately.Let the pizza cook for 7 minutes. Open the oven and, using the peel, rotate the pizza. Cook for an additional 5 minutes, or until the top crust is browning in spots and the onion cream is drying out near the crust.
Remove the Buffalo cauliflower pizza from the oven. Cut it into slices and sprinkle the arugula and green onions on top. Drizzle with the vegan ranch as well. Enjoy immediately!