Preheat your oven to 425°F (220°C). Line the baking sheet with aluminum foil if desired for easy cleanup.
In a mixing bowl, combine the olive oil, garlic powder, onion powder, thyme, smoked paprika, salt, and pepper. Mix well to create a marinade.
Add the chicken thighs to the bowl and coat them thoroughly with the marinade. Allow them to marinate for about 10 minutes while you prepare the vegetables.
On the prepared baking sheet, arrange the broccoli florets, baby carrots, and red bell pepper slices. Drizzle with a little olive oil and sprinkle with salt and pepper. Toss the vegetables to coat evenly.
Nestle the marinated chicken thighs among the vegetables on the sheet pan.
Place the baking sheet in the preheated oven and bake for 30-35 minutes, or until the chicken is cooked through (internal temperature reaches 165°F or 75°C) and the vegetables are tender.
Once cooked, remove the sheet pan from the oven and let it rest for a few minutes. Garnish with lemon slices before serving.