1. Add the Dijon mustard, garlic, onion powder, soy sauce, olive oil, and balsamic vinegar together in a large plastic bag or shallow dish. Season both sides of the steak with salt and pepper then add the steak to the marinade. Let it marinate for 2 hours or overnight in the refrigerator.

2. When ready to grill, brush the grill grates with oil and heat the outdoor grill to high heat (450°F). Remove the flank steak from the marinade and shake off excess, but do not discard marinade.

3. Add the flank steak to the hot grill and close the lid. Cook for 3-5 minutes on each side for medium-rare steak, or until the internal temperature reaches 135°F.

4. Brush the zucchini with olive oil and sprinkle with salt. Add the zucchini to the grill when you flip the steak and grill for 2-3 minutes on each side until tender and charred.

5. Remove the steak and zucchini to a clean cutting board and let the steak rest for 10 minutes.

6. While the steak rests, add the reserved marinade to a saucepan and bring it to a rolling boil over medium-high heat. Reduce to a simmer and cook for 2-3 minutes until thickened into a glaze.

7. Add the feta and heavy cream to a blender or food processor and blend until smooth and creamy.

8. Brush half of the balsamic glaze over the steak then slice thinly against the grain.

9. Spread whipped feta on plates and top with grilled steak and zucchini. Drizzle with remaining balsamic glaze and serve.