Preheat your oven to 400°F (200°C) or heat up a grill to medium-high. Combine the ground beef with garlic powder, salt, and black pepper in a mixing bowl.

Divide the mixture into four equal portions and shape each portion into a thick patty, placing each in the center of its foil sheet.

On each patty, lay a slice of Swiss cheese, then add mushrooms, onions, and bell peppers. Optionally, add potatoes or zucchini around the patties.

Fold the foil around the patties tightly, leaving space inside for steam. Optionally double-wrap the packets to enhance moisture.

Place the foil packets on a baking sheet or grill grates and cook for about 25 minutes, monitoring their progress until the beef reaches 160°F.

Carefully unwrap the foil packets and serve hot, straight from the foil.