Place oven racks in upper and lower third of oven and preheat to 425 F. Line 2 rimmed baking trays with parchment paper and set aside.

In small bowl, whisk together avocado oil, harissa paste, smoked paprika, and ground cumin until well combined. Set aside.

Scatter Brussels sprouts, cauliflower, and red peppers over one of the prepared baking trays in a single layer. Scatter leeks, chickpeas, and halloumi cheese on second baking tray. Evenly drizzle spice mixture over each baking tray and toss until evenly coated. Place tray with Brussels sprout mixture on lower rack of oven and tray with chickpea mixture on upper rack. Roast until vegetables are fork tender and halloumi is golden brown, about 30 to 45 minutes.

Meanwhile, make couscous side. In medium-sized, heat-proof bowl, place couscous. Pour boiling water over couscous and cover with plate to trap the steam. Set aside for 5 minutes.

In another medium bowl, whisk together lemon zest, lemon juice, olive oil, and salt. Add kale and, with clean hands, massage dressing into kale for a minute. Fluff couscous with a fork and add to kale mixture, tossing well to combine.

To serve, gently toss together roasted vegetables, chickpeas, and halloumi on one baking tray. Serve alongside couscous.