Preheat and Prep:
Preheat grill to medium-high or oven to 425°F (220°C). Cut 4 large sheets of heavy-duty foil (about 12x12 inches each).
Season the Ingredients:
In a large bowl, toss steak cubes and potatoes with olive oil, garlic, Italian seasoning, salt, and pepper.
Assemble Foil Packs:
Divide steak and potatoes evenly among the foil sheets. Drizzle each with melted butter and sprinkle with thyme or rosemary.
Seal and Cook:
Fold up each foil packet tightly to seal.
Grill: Place packets on the grill and cook for 10–12 minutes per side.
Oven: Bake directly on a baking sheet for 20–25 minutes, or until potatoes are tender and steak is cooked to desired doneness.
Serve:
Carefully open foil packs (watch the steam!) and garnish with chopped parsley if desired. Serve hot.