In a large bowl, whisk together the ½ cup Greek yogurt, 3 tablespoons olive oil, 2 cloves minced garlic, 1 tablespoon shawarma spice, 1 teaspoon sumac, 1 teaspoon curry powder, 1 teaspoon onion powder, 1½ teaspoons salt, 1 teaspoon black pepper, 2 tablespoons pomegranate molasses.
Add the 3 pounds sliced chicken and turn to coat every piece. Let them marinate for at least 30 minutes, or up to overnight in the fridge. The yogurt tenderizes the chicken while the spices and that pomegranate molasses soak in, which is what gives you deep flavor and serious char.
When you are ready to cook, preheat your oven to 425°F (220°C) and line a large rimmed baking sheet with foil.
Toss the sliced sweet onion and halved Campari tomatoes with the 3 tablespoons olive oil and ¼ teaspoon salt.
Toss the marinated chicken, onions, and tomatoes together on the sheet pan in a single layer. Give everything room so it roasts instead of steams.
Roast for 20 to 22 minutes, until the chicken reaches 165°F (74°C). Tenderloins are lean breast meat, so 165°F is the right pull here, not higher, or they dry out.
Switch the oven to broil for 2 to 3 minutes, until the edges of the chicken char and caramelize. Watch it closely, because the pomegranate molasses are sugary and go from beautifully charred to burnt fast.
Let the chicken rest for 5 minutes, then serve in warm pita or over rice with a side of hummus, drizzle additional pomegranate molasses, garlic sauce or top it with chopped parsley and a squeeze of lemon.