To roast the squash: On your prepared baking sheet, toss the cubed butternut in enough olive oil to lightly coat all sides, about 2 tablespoons. Sprinkle with 1 teaspoon chili pepper and a pinch of salt and pepper. Arrange the butternut in a single layer. Bake until the butternut is tender throughout and caramelized on the edges, about 30 to 35 minutes, tossing halfway.
Meanwhile, to assemble the slaw: In a medium mixing bowl, combine the cabbage, black beans, green onion, cilantro, lime juice, olive oil and salt. Toss to combine, then taste and add additional lime juice and/or salt if necessary. Set aside to marinate.
To prepare the guacamole: In a small bowl, combine the diced avocado, lime juice, coriander and salt. Mash with a pastry cutter, potato masher or fork until the mixture is blended and no longer chunky. Taste and add additional salt if necessary.
To warm the tortillas: In a small skillet over medium heat, warm each tortilla on both sides before transferring to a plate and covering with a lint-free towel to keep warm. Repeat with each tortilla, stacking each warmed tortilla on the last.
To assemble the tacos, spoon an ample amount of slaw down the center of your taco, top with roasted butternut and spread a spoonful of guacamole down the side. Top with garnishes of your choice and serve immediately