Preheat the oven to 400 degrees F. Lightly grease a large baking sheet (or line with a silicone baking mat) and set aside.
Place the cauliflower, chickpeas, and red onion in a large bowl, drizzle with olive oil, and sprinkle with the chili powder, chipotle chili powder, cumin, garlic powder, and salt. Toss to evenly coat, then spread in a single layer on the prepared baking sheet. Bake for 30 to 35 minutes, stirring twice, until the chickpeas are crispy and the cauliflower is just tender. Remove from the oven and set aside.
To serve, fill the taco boats with the warm cauliflower and chickpea mixture. Sprinkle on any desired toppings. Enjoy immediately.
The filling tastes best the day the tacos are made but can be reheated the next day, either in the microwave or in an oven preheated to 350 degrees F.