In a microwave safe bowl add the oil, soy sauce, garlic halves and sprigs of thyme. Microwave for 30 seconds to warm the mixture so the flavours infuse. Cool.
Add the steaks to the marinade and leave for 2 hours at room temperature. Turn every 30 minutes.
Heat the barbecue to hot. Remove the steak from the marinade and remove any residual garlic and thyme if desired. Lightly salt and pepper both sides of the steak. Add to the hot grill and cook until good grill marks are on the first side, turn the steak and do the same on the other side. Rest for 3 minutes then serve. (You can cook longer based on your preferred doneness.)