Yes, you can cook couscous in the oven! It's added to the sheet pan after the chickpeas, cauliflower, and carrots spiced with ras el hanout have roasted for a spell. Feta, cilantro, and a squeeze of lemon help bring all the flavors together.
Preheat oven to 475 degrees, with a rimmed baking sheet on center rack. Toss chickpeas, cauliflower, and carrots with oil and ras el hanout. Transfer to hot baking sheet with lemon halves, cut-sides up; season with salt and pepper. Roast until browned and mostly tender, 30 minutes. Remove from oven; reserve lemon.
Reduce heat to 350 degrees. Add couscous, 2 cups boiling water, and 1 teaspoon salt to baking sheet; stir. Wearing oven mitts, cover sheet with parchment-lined foil, crimping tightly around edges; carefully return to oven. Cook until liquid is absorbed, 10 minutes. Remove from oven and let cool, covered, 5 minutes. Remove foil; squeeze reserved lemon over couscous and fluff with a fork. Top with feta, cilantro, and a drizzle of oil; serve.