Adjust rack to top position and preheat oven to 425 degrees. Wash and dry all produce. Zest and quarter lemon (quarter both lemons for 4 servings). Mince or grate garlic. Finely chop cilantro leaves and stems. Trim, peel, and cut carrots on a diagonal into 1/2-inch-thick pieces.

Toss carrots on a foil-lined baking sheet with a large drizzle of olive oil, salt, and pepper. Roast on top rack until golden brown and softened, 20-25 minutes.

Meanwhile, in a small bowl, combine cilantro, half the cumin, half the lemon zest, juice from half the lemon (whole lemon for 4 servings), 2 TBSP olive oil (4 TBSP for 4), and up to half the garlic to taste (you’ll use more later). Season with salt, pepper, and chili flakes to taste.

Place a small pot over mediumhigh heat. Add 1 TBSP plain butter (2 TBSP for 4 servings), couscous, and remaining garlic. Cook, stirring often, until garlic is fragrant and couscous is lightly toasted, 1-2 minutes. Stir in 3/4 cup water (11/2 cups for 4) and stock concentrate. Bring to a boil, then cover and reduce to a low simmer. Cook until al dente, 6-8 minutes. Keep covered off heat until ready to serve.

Heat a large drizzle of olive oil in a large, preferably nonstick, pan over medium-high heat. Pat barramundi dry with paper towels. Season generously with salt, pepper, and remaining cumin. Add barramundi and cook until fish is opaque and cooked through, 4-6 minutes per side. Turn off heat.

Fluff couscous with a fork; stir in garlic herb butter and season with salt and pepper. Toss carrots with remaining lemon zest. Divide couscous, carrots, and barramundi between plates. Top barramundi with chimichurri. Serve with remaining lemon wedges on the side.