Prepare your Blackstone OpenFlame with a bed of hot coals. Adjust the grill grate to medium heat—you should only be able to hold your hand over it for about 5 seconds.
On a large sheet of foil, place the potatoes in the center. Top with garlic and rosemary, drizzle with olive oil, and season generously. Wrap tightly into a foil pouch and place over medium heat.
Lightly score the surface of the ribeye with a sharp knife. Drizzle with olive oil and season generously on all sides.
Place the steak over the coals and cook for 10–15 minutes. Adjust the grate height as needed to prevent burning. Flip and cook another 10–15 minutes, or until desired doneness (about 130°F for medium-rare). Remove and let rest.
Season zucchini and squash with oil and seasoning. Lower the grate closer to the coals and cook cut-side down for 3–4 minutes. Flip and cook another 3–4 minutes.
In a bowl, mix all sauce ingredients until combined.
Once potatoes are tender, slice the steak and vegetables. Serve with the roasted potatoes, garlic, and sauce on the side.
