Place chicken* in a large pot with enough salted water to cover by 2 inches. Cover and bring to a boil; cook until mostly cooked through, 5-8 minutes (it’ll finish cooking later).

Turn off heat. Drain and transfer chicken to a cutting board; wipe out pot.

While chicken cooks, wash and dry produce.

Peel, trim, and halve carrot lengthwise; thinly slice into half-moons. Halve celery lengthwise and thinly slice crosswise. Peel and mince or grate garlic. Trim and thinly slice scallions, separating whites from greens. Zest and quarter lemon. Pick and finely chop fronds from dill.

Heat a drizzle of oil in pot used for chicken over medium-high heat. Add carrot, celery, a big pinch of salt, and pepper. Cook, stirring occasionally, until veggies are lightly browned and slightly softened, 3-5 minutes.

Add garlic and scallion whites; cook, stirring, until fragrant, 1 minute.

Stir in 3½ cups of water (6 cups for 4 servings), couscous, and stock concentrates, scraping any browned bits from bottom of pot. Cover and bring to a boil, then immediately reduce heat to a low simmer. Cook, covered, until couscous is tender, 7-9 minutes.

Once chicken is cool enough to handle, using two forks, shred into bite-size pieces. Return chicken to pot with couscous (add chicken even if couscous is not done); cook until chicken is cooked through, 2-3 minutes. Remove pot from heat.

Stir in scallion greens, crème fraîche, lemon zest, and juice from half the lemon (whole lemon for 4 servings). Season generously with salt (start with 1 tsp, then taste and add more from there if desired) and pepper.

Divide soup between bowls; squeeze juice from remaining lemon over top to taste and garnish with dill. Serve with any remaining lemon wedges on the side.