Preheat the oven to 200°C,180°Fan, Gas Mark 6 for 5 minutes.
Meanwhile, place the prepared vegetables including the garlic in a small shallow roasting pan lined with baking parchment paper. Add 1 teaspoon of the oil and a sprig of fresh thyme or rosemary leaves. Toss well and roast for 15 minutes.
5 minutes before the vegetables are ready, heat a non-stick griddle or frying pan over moderate heat until hot. Brush the steak with the remaining oil, season with black pepper and quickly sear in the hot pan for 1-2 minutes on one side.
Remove the roasting pan from the oven, gently toss the vegetables and position the steak on top of the vegetables.
Return the roasting pan to the oven and roast for a further 4 minutes, (for medium) or until the steak is cooked through to your liking.
Remove the roasting pan from the oven, cover with foil and set to one side to allow the steak to rest for 2-3 minutes.
Prepare the mustard dressing by whisking all the ingredients in a small bowl or shaking in a small clean glass jar with a lid until combined.
Arrange the vegetables and sliced steak in a bowl. Drizzle with the mustard dressing and garnish with remaining herbs before serving.
