1. Start by making the marinade for the vegetables. Combine the cilantro, lime juice, olive oil, garlic, chipotle chiles, and soy sauce in a blender and puree until smooth.
2. Pour marinade into a large zip-lock bag and add the chopped squash, peppers, and scallions. Press excess air out of the bag, seal, and shake to coat veggies evenly with the marinade. Let vegetables marinate at room temperature while you heat your grill to medium-high heat (about 20-25 minutes).
3. While vegetables marinate, make your salsa by combining the avocado, tomato, chile, lime juice, chopped shallot, and salt in a bowl and mixing well.
4. When grill is hot, skewer the vegetables on metal or wooden skewers (if using wood, make sure to soak in water first so they don’t catch fire) so they can be easily cooked on the grill. You can reserve any excess marinade to use as a sauce on your tacos.
5. Place vegetable skewers on the grill and cook, turning periodically until veggies are tender and beginning to char, about 20 minutes.
6. Once vegetables are cooked, remove from grill, cool slightly, and remove from skewers. Place tortillas on the grill quickly to warm, flipping once.
7. Assemble tacos by placing some of the grilled vegetables on each tortilla. Top with avocado salsa, queso fresco, and fresh cilantro.