For the cauliflower: Trim off the leaves and a small part of the stem, leaving as much stem intact as possible. Cut the cauliflower into 8 wedges, making sure to include part of the stem in each wedge. Don’t worry if pieces fall off—use them too. Heat about 1 inch of water in a large pot fitted with a steamer basket over medium-high heat. Place the cauliflower in the basket, cover, and cook until a knife pierces the cauliflower without hesitation, about 4-5 minutes. Carefully remove the cauliflower from the basket, place on a large oven-safe skillet (cast iron works great here), and brush with olive oil. Transfer to a pizza oven or an oven rack with a preheated broiler, cooking until the cauliflower is charred.
For the chile-walnut paste: Place all of the ingredients in a small bowl and stir to combine. Alternatively, if you’d like a smoother paste, use a mortar and pestle or a food processor to blend everything together.
For the scallions: Here’s another technique I picked up from Kim’s book. Start by thinly slicing the scallions on a bias. Place them in a colander and run under cold water for a few minutes to rinse off any slime, then transfer to a clean towel. Gently dry the scallions as well as you can, then transfer to a separate towel to air-dry for 10 more minutes. If prepping the scallions in advance, store them in the refrigerator with a small towel or paper towel in a sealed container.
To assemble: Spread the walnut paste over the top sides of the cauliflower. Flip, and repeat on the other sides. If any florets break off, toss them in the paste as well. Transfer the cauliflower to a serving bowl and top with the scallions.