Heat the oven: Preheat the oven to 425°F with a rack in the middle. Set out a large rimmed sheet pan.

Set up the pan: Line the sheet pan with parchment or foil for easier cleanup.

Pat the chicken thighs dry with paper towels. If a few pieces are much thinner on one end, fold the thin end under so the chicken cooks more evenly.

Prep the vegetables: Trim the green beans if needed. Halve any large mushrooms. Slice the red onion into 1-inch wedges. Slice the scallions and set them aside for serving.

Spoon 2 tablespoons of the glaze into a small bowl and set it aside for the green beans later.

Coat the chicken: Add the chicken thighs to the large bowl with the remaining glaze. Turn the chicken so all sides are coated well.

Put the mushrooms and red onion on the sheet pan. Drizzle them with the remaining 1 tablespoon olive oil and toss on the pan to coat them lightly.

Spread the mushrooms and onion into an even layer, leaving a few open spaces in the center of the sheet pan.

Build the sheet pan: Lift the chicken thighs from the bowl and place them in the open spaces on the sheet pan, smoother side up. Discard any glaze left in the bowl that touched the raw chicken.

Start roasting: Roast for 12 minutes.

While the chicken starts cooking, put the green beans into the small bowl with the reserved glaze and toss to coat them.