1.In a shallow dish, marinate steak in combined oil and balsamic glaze for at least 20 minutes. Season.
2.Preheat a char-grill pan or barbecue on high. Grill steak for 2 minutes each side until cooked to taste. Rest, loosely covered with foil, for 5 minutes, then thinly slice.
3.In a large salad bowl, combine watermelon, spinach, radish, avocado and mint. Top with steak and crumble feta over. Drizzle with extra glaze to serve.
✦ For a no-cook meal, substitute cooked prawns for beef and lime juice for balsamic glaze.