Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce.

Trim, peel, and cut carrots on a diagonal into ½-inch-thick pieces. Trim and quarter Brussels sprouts lengthwise (halve any smaller sprouts). Halve, peel, and cut onion into ½-inch-thick wedges.

Toss carrots, Brussels sprouts, and onion on a baking sheet with a large drizzle of oil and chili flakes to taste; season with salt. Roast on top rack until carrots are tender and Brussels sprouts are lightly charred, 18-20 minutes.

Meanwhile, trim and thinly slice scallions, separating whites from greens. Peel and mince or grate garlic.

Pat chicken* dry with paper towels and season all over with salt and pepper.

Heat a drizzle of oil in a large pan over medium-high heat. Add chicken; cook until browned and cooked through, 5-7 minutes per side. Transfer to a cutting board; reserve pan.

Heat 2 TBSP butter (4 TBSP for 4 servings) in pan used for chicken over medium heat. Add scallion whites and garlic; cook, stirring, until fragrant, 30 seconds.

Stir in honey, miso sauce concentrate, and ¼ cup water (½ cup for 4). Bring to a simmer and cook, stirring occasionally, until glaze has thickened slightly, 2-3 minutes more. (TIP: If glaze does not come together, stir in a splash of water.) Taste and season with salt and pepper if desired.

Once veggies are done roasting, sprinkle with sesame seeds; toss to coat.

Thinly slice chicken crosswise.

Divide chicken and veggies between plates. Drizzle chicken with glaze and sprinkle everything with scallion greens. Serve.