To make the marinade, mix together the oil, vinegar, mustard, garlic, basil, oregano, chilli flakes and pepper in a small bowl.
Place the steaks in a dish just large enough to hold them in one layer and pour over the marinade. Turn the steaks in the marinade to coat both sides. Cover and leave to marinate in the fridge for at least 2 hours.
Remove the steaks from the refrigerator and allow to come to room temperature. Pour off the marinade into a small bowl. Prepare a charcoal fire, setting the rack 10–13 cm above the heat, or preheat the grill to high.
Place the steaks on the barbecue, or under the grill, and cook for about 6 minutes on each side for medium, or to taste. Meanwhile, using a small brush, coat the vegetable pieces with the reserved marinade.
Transfer the steaks to a platter, cover with foil and keep warm. Add the vegetables to the barbecue or grill and cook until browned and softened, turning once and brushing twice with the remaining marinade. Serve the vegetables with the steaks.