Set up your barbecue for direct cooking. Place a casserole dish (without lid) in the centre of the grill and add the oil. Preheat on high for ten minutes.
Oil the drumsticks and season with salt and pepper.
Once the barbecue is preheated, leave the heat setting on high. Add the onion and garlic to the casserole dish and cook, stirring occasionally, for 2-3 minutes. At the same time, add the chicken to the grill and cook for 2-3 minutes per side. Once you have turned the chicken, remove the casserole dish from the barbecue.
Add the undrained tomatoes and stock to the casserole and stir through.
Turn your barbecue to the roast setting (add a convection tray and trivet if using a Q) using tongs and/or heat proof gloves. Place the lid on the casserole dish and place on barbecue. Cook for 1 hour.
Remove the casserole dish lid and cook for a further 25-30 minutes, or until the chicken is tender and the sauce has reduced and thickened slightly.
Add the olives, parsley and oregano and cook for a further 5-10 minutes or until heated through.