Prep the Veggie Packets: Take a large 36x18-inch / 90x45 cm piece of heavy-duty foil and fold it in half.
In the center, combine the sliced sweet peppers and onion.
Drizzle with 1 tablespoon / 15 ml of olive oil, 1 teaspoon / 4 g (0.14 oz) of fajita seasoning, and all the minced garlic.
Toss to coat. Create a second foil packet of the same size for the mushrooms and zucchini.
Drizzle them with the remaining 1 tablespoon / 15 ml of oil and 1 teaspoon / 4 g (0.14 oz) of fajita seasoning. For both packets, bring the long edges of the foil together and seal with a double fold, then fold and seal the short ends, leaving some space inside for steam to circulate.
Wrap the stack of tortillas in a separate piece of foil.
Grill the Peppers & Onions: Preheat your grill to medium heat, about 350-450°F / 175-230°C (450°F).
Place the pepper and onion packet directly on the grill rack.
Grill for 20 minutes, flipping the packet once halfway through.
Grill the Zucchini, Mushrooms & Tortillas: About 10 minutes into the pepper packet's cooking time, add the mushroom-zucchini packet and the foil-wrapped tortillas to the grill.
Grill for the remaining 10 minutes, flipping them once, until the vegetables are tender and the tortillas are warm and soft.
Make the Easy Guacamole: While the veggies grill, prepare the guacamole.
In a bowl, mash the avocado with the sour cream, cilantro, lime juice, and salt until it reaches your desired consistency. Gently stir in the diced tomato and green onion.
Assemble and Serve: Carefully open the hot foil packets, watching for steam.
Serve the sizzling vegetables family-style with the warm tortillas, shredded cheese, fresh guacamole, and any other desired toppings like cilantro, salsa, and sour cream.
Slice all your veggies up to 2 days in advance and store them in an airtight container in the fridge to make assembly on grilling day super fast.
Add a pinch of smoked paprika or a drop of liquid smoke to the vegetable packets before sealing to enhance that classic grilled, smoky flavor.