Prepare the Oven and Cauliflower: Preheat your oven to 425°F (220°C). Arrange the cauliflower florets evenly on a nonstick baking sheet. Lightly spray them with olive oil, then season with a pinch of sea salt and freshly cracked black pepper. Roast in the oven for about 15 minutes, or until the cauliflower starts to turn golden and gets a little crisp around the edges.
Make the Kung Pao Sauce: While the cauliflower roasts, whisk together the soy sauce, hoisin sauce, sherry vinegar, toasted sesame oil, brown sugar, cornstarch, minced garlic, and freshly grated ginger in a small bowl. Whisk thoroughly to dissolve the cornstarch completely and combine all ingredients into a smooth sauce.
Toss Cauliflower with Sauce and Chiles: Remove the baking sheet from the oven. Scatter the dried chiles de árbol over the cauliflower, then pour the prepared sauce evenly over the top. Use tongs or a spatula to gently toss the cauliflower, making sure each piece is well coated with the sauce.
Continue Roasting with Sauce: Return the baking sheet to the oven and roast for another 15 to 20 minutes. Stir and toss the cauliflower every 5 to 10 minutes to prevent the sauce from burning on the edges and to help it thicken and glaze the florets nicely.
Final Touches and Serving: Once the cauliflower is tender, glossy, and perfectly coated in sauce, remove the pan from the oven. Sprinkle the chopped peanuts and sliced green onions over the top. Serve immediately on its own or over a bed of warm jasmine rice.