Preheat the oven to 425 degrees and line a baking sheet with parchment paper.
Add butternut squash, red onion, olive oil, taco seasoning and red pepper flakes to the baking sheet and toss to coat evenly. Place in the oven and bake for 20 minutes (flipping halfway).
While the veggies are roasting, prepare the chipotle cilantro sauce. Add all of the ingredients to a blender or food processor and pulse until combined.* Taste and adjust seasonings as needed. Set aside.
Heat the tortillas over an open flame (or in the oven/microwave) and assemble the tacos.
Layer lettuce, cabbage, avocado and roasted veggies in each tortilla. Top with a drizzle of chipotle cilantro sauce and serve with additional cilantro and lime wedges.
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Notes
*Be sure to add the chipotles and chipotle sauce a little at a time to make sure it isn't too spicy for you.