Make the salsa. Place the tomatoes, garlic, onion, tomato paste, Turkish red pepper paste, harissa, paprika, cumin, lemon zest, lemon juice, pepper, & salt into a food processor. Blend until you have a smooth paste.
Separate the salsa. Remove half of the salsa, then place it into an airtight container and store in the fridge until your ready to cook the chicken. I'll explain more about the reason for this later in the recipe.
Finish the Marinade. Place the other half of the salsa into a large bowl. Add the yogurt, parsley, & honey⏤Stir to combine everything. Add the drumsticks into the marinade⏤toss to coat. Add the bay leaves and cover the bowl. Allow the chicken to marinate in the fridge overnight.
Heat the BBQ. Prepare your grill for indirect cooking, creating a zone of direct high heat & a second zone of indirect heat. If using a gas grill, begin preheating at least 15 minutes before grilling. If using charcoal, light the charcoal at least 30 minutes before grilling
Grill the chicken. Place the chicken on the indirect side of the grill, as close to the fire as possible without being over the direct heat. Cook the chicken, rotating the pieces 180 degrees every 15 minutes, until an instant-read thermometer inserted in the thickest part of the chicken (without hitting the bone) registers a temperature of 165ºF. Depending on the size of your chicken & the temperature of your grill, this could take as little as 35 minutes or up to 45 minutes.
Remove the chicken from the grill and allow it to rest for 5-10 minutes before serving. This allow for the juice to distribute through the chicken.
Grill the bread. Add a tablespoon of the leftover salsa on each flatbread, spread it over the top, sprinkle with nigella seeds, place the bread on the grill, and heat up for a few minutes⏤soft and warm, remove from the heat.
Assemble the Meal. Prepare the sumac onion as directed. Layer the chicken on the flatbread, then top with the sumac onions and add garlic mayo if using.