Prepare an outdoor grill, preferably a charcoal grill, for medium-high heat.
Place potatoes in a microwave-safe dish and cook on high until they are tender with a bite, about 3 minutes.
Divide steak, potatoes, onions, red and green bell pepper, and carrots evenly onto 4 to 6 squares of aluminum foil. Add 1 tablespoon butter and a little fresh garlic to each pack; fold foil over the top to close each packet tightly.
Place foil packs on the hot side of the grill. Cook for 5 minutes. Carefully open one foil pack to check for steak doneness.
If steak is not cooked to your taste after 5 minutes, continue to cook, checking for doneness every few minutes. An instant-read thermometer inserted into the center will read 130 degrees F (54 degrees C) for medium rare.
4 servings