Line a sheet pan with parchment paper. Scatter the asparagus, carrots, scallions, potatoes and garlic evenly on the tray. Drizzle with olive oil and season with salt and pepper.
Brush the chicken liberally with the mustard glaze and drizzle a little glaze over the vegetables as well. Scatter the thyme sprigs over the vegetables and the chicken.
Roast for 30-35 mins, rotating the pan occasionally to be sure the vegetables roast evenly. Remove when the chicken is cooked through and the skin is browned and crispy.