Preheat the oven to 180C/350F/Gas 4.
For the ostrich, heat the oil in an ovenproof frying pan and season the steak well with salt and freshly ground black pepper. Place into the pan with the garlic and rosemary and sear on all sides. Transfer to the oven to continue cooking for about 6-8 minutes, or until cooked to your liking.
For the sautéed potatoes, cut the potatoes into 1cm/½in thick slices. Heat the oil in an ovenproof frying pan and add the potatoes, garlic and salt and freshly ground black pepper. Fry until the potatoes begin to colour. Transfer to the oven to continue cooking for about five minutes, until tender.
For the roast tomatoes, heat the oil in an ovenproof frying pan. Add the tomatoes and herbs to the pan and sear on all sides. Sprinkle over the balsamic vinegar and transfer to the oven to cook for about six minutes, or until soft.
To serve, cut the ostrich into three pieces and place onto a serving plate with the sautéed potatoes, green beans and roasted tomatoes.