Preheat the oven to 400°F. Spray a rimmed baking sheet with nonstick cooking spray. Place the cauliflower, Brussels sprouts and leeks on the baking sheet, drizzle over 2 tablespoons olive oil, sprinkle with salt and toss. Spread out on the sheet and bake for about 20 minutes, until the vegetables are tender and just slightly golden.
While the vegetables are roasting, make the spicy drizzle. Place the rest of the olive oil, Sriracha, parsley and sage in a blender or a food processor and blend until it is fairly smooth.
Transfer the vegetables to a serving platter, and either drizzle over the spicy sauce, or pass it on the side, or drizzle over a little and pass the rest (that’s what I usually do, but if you think some of your gang won’t go for it, leave it on the side). Serve hot, warm or room temperature.
Notes
Feel free to use any sort of drizzle here if this one isn't to your taste. I often serve roasted veggies plain or use whatever sauce is in the fridge.