Heat a large skillet/frying pan on medium high heat. Drizzle with olive oil and, working in batches, add the cauliflower wedges, cut side down, to the pan. Press the cauliflower onto the hot surface, and cook until deeply golden, about 5 to 6 minutes. Turn the cauliflower over to cook the other cut side, seasoning with a pinch of sea salt, until golden, another 5 to 6 minutes. Transfer the cauliflower, including any straggly bits, to a plate and set aside.
Return the skillet to medium heat. Add another drizzle of oil, and add the onions, and cook for 3 to 4 minutes until softened. Add the garlic and and chili crisp and stir for 30 to 45 seconds until fragrant. Pour in the tomatoes and add the salt and sugar and stir to combine. Cover and cook for 4-5 minutes to allow flavors to meld.
Place the cauliflower wedges into the sauce, cover and simmer on medium low for 10 to 15 minutes, until the cauliflower is tender all the way through (the exact time will depend upon the size of your wedges - test by inserting a skewer).
Top with scallions and more chili oil. Serve as is or with bread to mop up the sauce.