Heat oil in a small pan over medium heat. Add the garam masala, chilli powder, cumin, and turmeric. Cook, stirring, until fragrant, for 2 –3 minutes. Let cool.
Combine the spices with yoghurt, lemon juice, garlic, ginger, and salt. Coat the chicken thoroughly with the marinade, cover, and chill for at least one hour or up to 8 hours. Remove from the fridge and let sit at room temperature while preparing the barbeque.
Prepare the barbeque for direct high heat and indirect heat. Preheat for around 15 minutes. Oil the grill.
Place the chicken on the indirect heat side of the barbeque, breast side up, as close to the fire as possible without being over the direct heat. Close the lid. Cook the chicken, rotating it 180 degrees every 15 minutes, until a thermometer, inserted in the thickest part of the breast (without hitting the bone), reads 75°c, and is cooked through. Depending on the size of your chicken, and the temperature of the barbeque, this could take as little as 30 minutes or up to 1 hour.
Move the chicken over direct heat, carefully flipping it so that it is skin side down and comes in direct contact with the grill grates. Cook 2-3 minutes longer, until the chicken skin is crispy and charred as desired. Alternately it can be finished under the grill for 2-3 minutes.
