Preheat your oven to 425°F (220°C).
In a large bowl, combine the zaatar spice blend, olive oil, garlic powder, onion powder, salt, and pepper. Mix well to form a marinade.
Add the chicken thighs to the bowl and coat them thoroughly with the marinade. Let it marinate for at least 30 minutes, or up to overnight in the refrigerator for more flavor.
While the chicken is marinating, prepare the vegetables. In a separate bowl, toss the chopped bell peppers, red onion, zucchini, and cherry tomatoes with olive oil, salt, and pepper.
Spread the marinated chicken thighs on a large baking sheet. Arrange the vegetables around the chicken.
Squeeze the lemon juice over the chicken and vegetables.
Roast in the preheated oven for 35-40 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (75°C) and the vegetables are tender.
Remove from the oven and let it rest for 5 minutes. Garnish with fresh parsley before serving.