Cut the potatoes into 1-inch chunks, then deseed and cut the green peppers into 1-inch pieces, and cut the onion into 1-inch wedges. Mince the garlic and finely chop the fresh rosemary. In a large bowl, combine all the vegetables with the olive oil, minced garlic, smoked paprika, Montreal steak seasoning, Italian seasoning, salt, black pepper, and fresh rosemary. Toss everything together until the vegetables are evenly coated with oil and seasonings. I like to massage the mixture with my hands for about 30 seconds to really work the seasonings into the potatoes—it helps develop better flavor.

Tear off two large sheets of heavy-duty aluminum foil (about 18 inches each). Divide the seasoned vegetable mixture evenly between the two foil sheets, piling the vegetables in the center of each sheet. Fold the foil up and over the vegetables, then seal the edges tightly by crimping and folding them together. Make sure the packets are well-sealed so steam can build up inside while grilling. I always double-check my seals by gently squeezing the packets—if I feel any steam escaping, I reseal that section.

Preheat your grill to medium heat. Place the sealed foil packets directly on the grill grates and cover the grill. Cook for 40-45 minutes, until the potatoes are fork-tender. You can gently shake the packets about halfway through cooking to redistribute the vegetables and ensure even cooking. The foil packet acts as a steamer, trapping moisture and heat to cook the vegetables perfectly while infusing them with all the seasonings.

Carefully open the foil packets, being mindful of the hot steam that will escape. Transfer the grilled vegetables to a serving dish or directly onto plates. Serve hot while the vegetables are still steaming.