In a mixing bowl, whisk together the Dijon mustard, pure maple syrup, olive oil, garlic powder, onion powder, dried thyme, salt, and pepper to prepare the glaze.
Pat the chicken thighs dry with paper towels. Toss the chicken in the glaze until well coated. In a separate bowl, toss the halved fingerling potatoes with a few spoonfuls of the glaze, coating them evenly but not drenched.
Spread the fingerling potatoes in a single layer on a rimmed sheet pan, leaving space between pieces. Nestle the chicken thighs skin-side up among the potatoes. Pour any remaining glaze over the chicken and potatoes.
Roast in a preheated oven at 425°F (220°C) for 35-40 minutes. Halfway through, use tongs to turn the potatoes for even browning. Chicken is done when skin is crispy and internal temperature reaches 165°F (74°C).
Remove from oven and sprinkle freshly chopped parsley over the chicken and potatoes. Serve hot and enjoy.
