Preheat the oven to 425°F (220°C).
In a large bowl, combine the halved baby potatoes, red bell pepper pieces, yellow bell pepper pieces, and red onion wedges.
Add 2 tablespoons of olive oil, garlic powder, smoked paprika, dried thyme, dried oregano, salt, and black pepper to the vegetables. Toss well to coat evenly.
Place the seasoned vegetables on a large rimmed baking sheet, spreading them out in an even layer.
Pat the chicken thighs dry with paper towels. Rub them with the remaining 1 tablespoon of olive oil and season both sides with salt and black pepper.
Nestle the chicken thighs skin-side up among the vegetables on the baking sheet.
Roast in the preheated oven for 35 to 40 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and the potatoes are tender and golden brown.
If desired, broil for an additional 2-3 minutes to crisp the chicken skin further, watching carefully to avoid burning.
Remove the sheet pan from the oven and let rest for 5 minutes.
Sprinkle the chopped fresh parsley over the chicken and vegetables before serving.