Preheat your oven to 425°F (220°C).
In a large mixing bowl, combine the olive oil, minced garlic, oregano, paprika, salt, and black pepper.
Add the chicken thighs to the bowl, and coat them evenly with the marinade. Let them sit for a few minutes while you prepare the vegetables.
On the large baking sheet, spread out the broccoli, bell peppers, and onion. Drizzle with a little olive oil and season with salt and pepper.
Place the marinated chicken thighs on top of the vegetables on the baking sheet.
Roast in the preheated oven for 25-30 minutes, or until the chicken reaches an internal temperature of 165°F (75°C) and the vegetables are tender.
If desired, squeeze lemon juice over the dish before serving.
Remove from the oven and let it rest for a few minutes before serving.