Preheat the oven to 425°F (220°C).
In a large bowl, combine the halved baby red potatoes, red bell pepper pieces, yellow bell pepper pieces, and red onion wedges.
Add 2 tablespoons of olive oil, 1/2 teaspoon garlic powder, 1/2 teaspoon smoked paprika, 1/2 teaspoon dried thyme, 1/2 teaspoon dried oregano, 1/2 teaspoon salt, and 1/4 teaspoon black pepper to the vegetables. Toss well to coat evenly.
Arrange the seasoned vegetables in a single layer on a large rimmed baking sheet.
In the same bowl, add the chicken thighs. Drizzle with the remaining 1 tablespoon olive oil and season with the remaining garlic powder, smoked paprika, dried thyme, dried oregano, salt, and black pepper. Rub the seasoning into the chicken skin.
Place the chicken thighs skin-side up on top of the vegetables on the baking sheet, ensuring they are spaced out and not touching.
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, switch the oven to broil for the last 2-3 minutes to crisp the chicken skin further, watching carefully to prevent burning.
Remove the sheet pan from the oven and sprinkle the chopped fresh parsley over the chicken and vegetables.
Let rest for 5 minutes before serving.