1. In a REC TEC Grills Matador, caramelize the onions in olive oil (4-5 minutes).
2. Add the spinach and cook until wilted; cool completely and drain any excess liquid.
3. On a cutting board, butterfly the flank steak being careful to not cut completely through the meat.
4. Season the flank steak with 2 tbsp of Ben's Heffer Dust and rub with garlic.
5. Add the spinach mixture evenly across the meat, then top with the chopped olives and feta cheese, and roll the flank steak tightly and secure with butchers twine.
6. Season the outside with 1 tbsp Ben's Heffer Dust.
7. Preheat REC TEC grill to 425°F with a sear kit, flat side up.
8. Sear on all sides and cook until the internal temperature reaches 135°F.
9. Let the flank steak rest for 15-20 minutes, then slice across the grain.