Add the tahini, water, olive oil, lemon zest and juice, sumac, paprika, coriander, oregano, mint, parsley, minced garlic, salt, and pepper to a mixing bowl and stir until well combined as a creamy marinade.
Reserve ¼ cup of the marinade and combine it with the yogurt in a separate bowl and mix until creamy. Set it aside for later.
Place the chicken thighs in a big bowl and season with salt and pepper on both sides.
Pour the rest of the tahini marinade over the chicken and toss until completely coated.
Cover the bowl with plastic wrap and place it in the fridge for at least 30 minutes or up to 2 hours.
Preheat the grill over medium-high heat.
Once hot, liberally oil the grates.
Cook the chicken thighs for 10 minutes on each side, or until the internal temperature reaches 175 F.