Adjust rack to middle position (middle and top positions for 4 servings) and preheat oven to 425 degrees. Bring a medium pot of salted water to a boil. Wash and dry all produce. Trim and thinly slice scallions, separating whites from greens. Zest and quarter lemon.

In a small bowl, combine panko, Parmesan, paprika, a large drizzle of olive oil, and a pinch of salt and pepper. Pat chicken dry with paper towels; season all over with salt and pepper. Evenly brush tops of chicken with sour cream. Mound panko mixture on top, pressing firmly to adhere.

Toss green beans on one side of a baking sheet with a large drizzle of olive oil and a pinch of salt and pepper. Place chicken, crust sides up, on opposite side of sheet. Roast until green beans are tender and chicken is cooked through, 15-17 minutes. (For 4 servings, divide between 2 baking sheets; roast green beans on top rack and chicken on middle rack.) TIP: If green beans are done before chicken is cooked through, remove from sheet and continue roasting chicken.

Once water is boiling, add couscous to pot. Cook until tender, 6-8 minutes. Drain thoroughly. Melt garlic herb butter in empty pot over medium heat. Add scallion whites and cook until softened, about 1 minute. Return cooked couscous to pot and stir to coat. Taste and season with salt and pepper.

Once green beans are done, remove from oven and toss with lemon zest and lemon juice to taste.

Divide chicken, green beans, and couscous between plates. Garnish chicken with scallion greens. Serve with remaining lemon wedges on the side.