Preheat the oven to 425°F (220°C).
In a large bowl, combine the halved baby red potatoes, broccoli florets, and red bell pepper pieces.
Add 2 tablespoons of olive oil, 1/2 teaspoon salt, 1/4 teaspoon black pepper, and 1/2 teaspoon garlic powder to the vegetables. Toss to coat evenly.
Place the seasoned vegetables on a large rimmed baking sheet, spreading them out in an even layer.
In the same bowl, add the chicken thighs.
Add 1 tablespoon olive oil, 1/2 teaspoon salt, 1/4 teaspoon black pepper, 1/2 teaspoon garlic powder, 1 teaspoon smoked paprika, and 1 teaspoon dried thyme to the chicken. Rub the seasoning all over the chicken thighs.
Nestle the seasoned chicken thighs on top of the vegetables on the baking sheet.
Arrange the lemon slices around and on top of the chicken and vegetables.
Place the baking sheet in the preheated oven and roast for 35 to 40 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and the potatoes are tender.
If desired, broil for an additional 2 to 3 minutes to crisp the chicken skin.
Remove from the oven and let rest for 5 minutes before serving.