Add the dijon, 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 teaspoons Dijon mustard, 4 cloves minced garlic, 2 teaspoons onion powder, 3 Tablespoons soy sauce or coconut aminos, 3 Tablespoons olive oil, 1/2 cup balsamic vinegar
When you’re 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. You need to cook down the glaze. 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, which allows for 5-10 degrees of carryover cooking while it rests.
Brush the zucchini with a little olive oil and sprinkle with salt. Add the sliced zucchini to the other side of the grill when you flip the steak and grill for 2-3 minutes on each side, until tender and charred in most spots. Press down on the zucchini with the tongs to help create grill marks.
3 large zucchini, 2-3 Tablespoons olive oil, Kosher salt to taste
Remove the steak and zucchini to a clean cutting board and let it rest for 10 minutes.
While it’s resting, make the balsamic glaze. Add the reserved marinade to a medium saucepan and bring it to a rolling boil over medium-high heat. This cooks off any bacteria from marinading to make it safe to eat. Make sure it’s a rolling boil of 165°F or higher. Reduce to a simmer and let it thicken into a glaze for 2-3 minutes, until it coats the back of a spoon. Add a splash more balsamic vinegar as needed.
Add the feta and heavy cream to a blender or food processor and blend until smooth.
8 ounces feta cheese, 3 Tablespoons heavy cream or milk
Brush half of the balsamic glaze on top of the steak then cut it thinly against the grain.
Spoon the feta on the bottom of the plate and top with grilled steak, zucchini, and drizzle with the remaining glaze and enjoy.