Barbecued za'atar chicken and lemon with tahini sauce

INGREDIENTS:

• 2.2kg whole chicken
• 125g butter, softened
• 1 tablespoon chopped fresh oregano leaves
• 2 teaspoons sumac
• 2 teaspoons ground cumin
• 2 teaspoons sesame seeds
• 1/2 teaspoon sea salt
• 1/2 teaspoon cracked black pepper
• 1 small garlic clove, crushed
• 1/2 cup hulled tahini
• 1/3 cup lemon juice
• 1/4 cup plain Greek-style yoghurt
• 1/3 cup finely chopped fresh flat-leaf parsley
• 3 Lebanese cucumbers, seeded, finely diced
• 2 tablespoons extra virgin olive oil
• 4 small lemons, halved, charred (see note)

INSTRUCTIONS:

• Step 1
  Preheat a barbecue (with hood) hotplate on medium heat, with hood closed.
• Step 2
  Pat chicken dry with paper towel. Place on a chopping board, breast-side down, with the cavity facing you. Using kitchen scissors, cut along both sides of the backbone and discard. Open out chicken. Turn over. Press down with the heel of your hand, to flatten.
• Step 3
  Place butter, oregano, sumac, cumin, sesame seeds, salt and pepper in a bowl. Mash with a fork until well combined. Run your finger between chicken skin and flesh on breast and legs to create a pocket. Push 1/2 the butter mixture under skin. Gently rub skin to evenly distribute butter.
• Step 4
  Cook chicken, skin-side down, on greased hotplate for 5 minutes or until skin is golden and crisp. Turn. Dollop with remaining butter mixture. Close hood. Cook for 45 to 50 minutes or until golden brown and cooked through. Transfer to a plate. Cover loosely with foil. Stand for 10 minutes to rest.
• Step 5
  Meanwhile, place garlic, tahini, 1/4 cup lemon juice, yoghurt, 1/2 the parsley and 1/4 cup water in a bowl. Season with salt and pepper. Stir to combine. Place cucumber, remaining parsley, oil and remaining lemon juice in a small bowl. Season with salt and pepper. Stir to combine.
• Step 6
  Cut chicken into pieces. Place on a serving platter. Spoon over cucumber mixture and serve with charred lemons and sauce.