Adjust rack to top position (top and middle positions for 4 servings) 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 halve zucchini lengthwise; slice crosswise on a diagonal into ½-inch-thick half-moons.

Toss carrots and zucchini on a baking sheet with a large drizzle of oil, half the garlic powder, half the thyme, salt, and pepper (for 4 servings, spread carrots out across entire sheet; use a second sheet for zucchini). (You’ll use the remaining garlic powder and thyme in Step 5.)

Roast on top rack, tossing halfway through, until browned and tender, 20-25 minutes. (For 4, roast on top and middle racks, swapping rack positions halfway through.)

While veggies roast, 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 heat. Add chicken; cook until browned and cooked through, 6-8 minutes per side. TIP: Lower heat and cover pan if chicken begins to brown too quickly.

Turn off heat; transfer to a cutting board. Wipe out pan.

Meanwhile, trim and thinly slice mushrooms (skip if your mushrooms are pre-sliced!).

In a small bowl, whisk together mustard, sour cream, stock concentrate, ¼ cup water, and 1 tsp vinegar (⅓ cup water and 2 tsp vinegar for 4 servings). (Be sure to measure the vinegar; we sent more.) Set aside.

Heat a drizzle of oil in pan used for chicken over medium-high heat. Add mushrooms and remaining thyme; season with salt and pepper. Cook, stirring occasionally, until softened, 2-4 minutes. Add remaining garlic powder and stir to coat.

Add mustard mixture and 2 TBSP butter (4 TBSP for 4 servings). Cook, stirring constantly, until butter has melted and sauce is thoroughly combined.

Bring to a simmer and cook, stirring constantly, until slightly thickened, 1-2 minutes more. TIP: If sauce is too thick, add a splash or two of water and bring to a boil; stir until smooth and slightly thickened.

Turn off heat and season with salt and pepper.

Thinly slice chicken crosswise.

Divide chicken and veggies between plates. Spoon mushroom sauce over chicken and serve.