Step 1

Place potatoes, onion, bell pepper, and mushrooms in a large bowl. Toss with garlic, olive oil, rosemary, salt, and pepper until everything is well distributed.

Step 2

Tear off 4 sheets of heavy duty foil (or 8 sheets of regular foil) that are large enough to hold ¼ of the vegetables with extra room to fold up the sides. If using regular foil, lay two sheets on top of each other to make a double layer.

Step 3

Spray the top foil sheet with cooking spray, and scoop ¼ of the vegetables onto it. Fold up the sides of the foil and twist to seal. Repeat with the remaining foil and vegetables, making 4 packets total.

Step 4

Heat a gas grill to low heat. Cook vegetables over low heat for 15 to 20 minutes, or until tender. Be careful when opening the foil packets, as hot steam may escape.