Make your cauliflower slices by removing the green leaves and most of the stem from the base. Leave some of the stem intact so the cauliflower doesn’t fall apart. Then, place the cauliflower, stem side down, and slice into the center with a large knife. Slice again on either side to create two flat pieces. Rinse and pat to dry. Reserve the small and broken florets for using later.
Place 1 tsp of sesame oil into the bottom of a cast iron pan. Place the cauliflower pieces into the pan, then drizzle the remaining 1 tsp of sesame oil over the cauliflower. Sprinkle with the salt and pepper. Place into the oven to roast for 20-25 minutes, checking after 20 minutes. Once it is nicely browned around the edges, carefully flip the pieces over and roast for 20 to 25 minutes more. It’s done when the edges are all perfectly crisp.
Whisk the Vegenaise and sriracha together, adjusting the heat level to your taste. Drizzle over the cauliflower and serve immediately.