Place the raw cashews in a bowl. Cover completely with boiling water. Set aside to soak for 30 minutes.
Preheat the oven to 400°F. Line a large baking sheet with parchment paper.
Chop the cauliflower into medium-small florets. Add to a large bowl and drizzle with oil. Toss to coat.
Add the chili powder, paprika, cumin, onion powder, garlic powder, and salt. Toss until every floret is evenly coated in the spice mixture.
Spread the cauliflower out on the prepared baking sheet in a single layer. Do not overcrowd.
Roast for 25 to 30 minutes, or until the tops start to turn golden brown. After 25 minutes, you can turn off the oven and let the cauliflower sit inside for 5 more minutes to finish gently without burning.
While the cauliflower roasts, prepare the slaw. Add the shredded purple cabbage, chopped cilantro, lime juice, Greek yogurt (or mayo), and salt to a large bowl. Toss well to combine. Taste and adjust seasoning. Set aside.
Drain and rinse the soaked cashews. Add to a high-speed blender along with the cilantro, lime juice, garlic, salt, and ½ cup water. Blend on high until completely smooth. Add more water a tablespoon at a time to reach your preferred drizzling consistency. Taste and adjust salt and lime.
Warm the tortillas in a dry skillet over medium heat or wrapped in a damp paper towel in the microwave.
Assemble the tacos: layer each warm tortilla with roasted cauliflower, a scoop of cilantro lime slaw, fresh pico de gallo, and sliced avocado. Drizzle generously with cilantro lime crema.
Serve immediately, with cilantro lime rice and black beans on the side if desired. Enjoy!