Thoroughly mix the mustard with all the other ingredients up to and including the pepper, set aside 2 tbsp. Brush the steaks with the remaining marinade, cover and marinate for approx. 30 mins.
Place the pepper and courgette in a bowl, add the oil, rosemary and salt, mix.
With the lid down, grill the vegetables over/on a medium heat (approx. 200 °C for approx. 10 mins. Grill the steaks with the vegetables, for approx. 5 mins. on each side. Remove the steaks from the grill, brush with the reserved marinade, serve with the vegetables.