Preheat your oven to 425°F (220°C).
In a mixing bowl, combine olive oil, garlic powder, paprika, dried thyme, salt, and black pepper. Mix well to create a marinade.
Add the chicken thighs to the bowl and coat them evenly with the marinade. Allow the chicken to marinate for about 5 minutes while you prepare the vegetables.
On the large baking sheet, arrange the halved baby potatoes, chopped red bell pepper, and sliced yellow onion. Drizzle with a little olive oil and season with salt and pepper. Toss the vegetables to coat.
Place the marinated chicken thighs on top of the vegetables on the baking sheet, skin side up.
Transfer the baking sheet to the preheated oven and roast for 35-40 minutes, or until the chicken is cooked through and the skin is crisp. The internal temperature of the chicken should reach 165°F (74°C).
Once cooked, remove the baking sheet from the oven and let it rest for a few minutes before serving.
Garnish with fresh parsley if desired, and serve the chicken thighs with roasted vegetables.