Adjust rack to top position, then preheat oven to 450 degrees. Wash and dry all produce. Thinly slice scallions, separating whites from greens. Trim, then halve zucchini lengthwise; cut crosswise into 1/2-inch-thick half-moons.

Heat a drizzle of oil in a small lidded pot over medium-high heat. Add scallion whites and cook until tender, 1 minute. Add couscous and a pinch of salt and pepper. Cook until toasted, 2-3 minutes. Add 3/4 cup water and bring mixture to a boil. Once boiling, cover, reduce heat to low, and cook until tender, 10-12 minutes. Keep covered until ready to serve.

Toss zucchini on a baking sheet with a drizzle of oil and a pinch of salt and pepper. Roast, tossing halfway through, until browned and tender, about 15 minutes. Remove from oven; cover until ready to serve.

Pat chicken dry with paper towels; season all over with salt and pepper. Heat a drizzle of oil in a large pan over medium-high heat. Add chicken and cook until browned and cooked through, 5-8 minutes per side. (TIP: If chicken darkens too quickly, reduce heat to medium.) Turn off heat; transfer to a plate.

Heat a drizzle of oil in same pan over medium heat. Add cranberries and cook, stirring, until slightly softened, 1-2 minutes. In a small bowl, combine stock concentrate, jam, and 2 TBSP water. Add to pan, bring to a simmer, and cook until thickened, 1-2 minutes. Turn off heat; stir in 1 TBSP butter until melted. Add chicken and turn to coat in sauce.

Fluff couscous with a fork, then stir in 1 TBSP butter and half the scallion greens. Season with salt and pepper. Divide couscous, zucchini, and chicken between plates. Top chicken with any remaining sauce. Garnish with remaining scallion greens.