Follow these step-by-step instructions to make your Juicy Grilled Flank Steak Rolls:

1. Prepare the Marinade: In a bowl, whisk together soy sauce, olive oil, balsamic vinegar, minced garlic, black pepper, and salt.

2. Marinate the Steak: Place the flank steak in a shallow dish or zip-top bag. Pour the marinade over the steak, ensuring it’s well-coated. Let this sit in the refrigerator for 30 minutes.

3. Prep the Vegetables: While the steak is marinating, slice the red bell pepper and zucchini into thin strips. Set them aside.

4. Remove Steak: After marinating, take the flank steak out of the fridge and allow it to reach room temperature for about 10 minutes.

5. Preheat the Grill: Heat the grill to medium-high heat, making sure the grill grates are clean and oiled to prevent sticking.

6. Grill the Steak: Place the flank steak on the grill and cook for about 4-6 minutes per side, depending on thickness. Aim for medium-rare to keep the meat juicy.

7. Rest the Steak: Once cooked, remove the steak from the grill and let it rest for about 5 minutes to allow juices to redistribute.

8. Slice the Steak: On a clean cutting board, slice the steak thinly against the grain to ensure tenderness.

9. Assemble the Rolls: Lay a slice of steak on a flat surface. Place a few slices of red bell pepper, zucchini, and a sprinkle of feta cheese in the middle.

10. Roll the Steak: Carefully roll the steak around the fillings, securing them inside. Use toothpicks if necessary to hold them together.

11. Grill the Rolls: Return the rolled steak back onto the grill for an additional 2-3 minutes to warm the fillings and enhance the grill marks.

12. Garnish and Serve: Once done, remove from the grill, discard any toothpicks, garnish with chopped parsley, and serve immediately.

Each step will guide you in creating a savory dish that showcases the vibrant flavors of the flank steak and fresh vegetables.