Preheat oven to 425°F. Line a rimmed sheet pan with parchment or foil.
Stir together garlic powder, smoked paprika, thyme, cumin, salt, and pepper in a small bowl.
Toss sweet potatoes and red onion with half the olive oil and about half the spice mix. Spread on the pan.
Whisk remaining olive oil with maple syrup and vinegar. Coat chicken with this mixture and the remaining spices.
Nestle chicken pieces among the vegetables on the sheet pan.
Roast for 20 minutes.
Stir vegetables and flip chicken. Roast 10–12 minutes more, until chicken reaches 165°F and potatoes are tender.
Broil 1–2 minutes for extra color, if desired.
Rest 5 minutes. Sprinkle with parsley and serve warm.