Preheat the oven to 375 degrees F and line 2 large baking sheets with parchment paper.
Place the cauliflower florets on one of the prepared baking sheets, breaking down any of the larger florets into smaller pieces.
In a small bowl, whisk together the avocado oil, smoked paprika, chipotle chili powder, cumin and salt until well combined. Pour over the cauliflower florets and toss until the cauliflower is evenly coated. Transfer to the oven and bake until the cauliflower is tender and golden brown, about 15 minutes, tossing halfway through.
Meanwhile, Pour the drained black beans and the salsa verde in a medium saucepan over medium heat and cook, uncovered and stirring occasionally, until the beans are tender, about 10 minutes.
Meanwhile, while all that is cooking along, place the tortillas in a single layer on the remaining prepared baking sheet. Brush the tops of each of the tortillas with avocado oil and transfer to the oven and bake until they are crisp throughout and golden brown on the edges, about 8 minutes.
When the beans are tender, transfer them to a bowl. Using a fork, mash until the beans are coarsely mashed. They don’t need to be completely smooth, but mashed enough to where they will easily spread on the tostada.
To serve: Spread the black bean mixture on the top side of each of the tostadas. Next, place the sliced avocado, then a small handful of the baby arugula. Top with the roasted cauliflower and garnish as desired (I topped with pickled red onions, sliced jalapenos, cilantro and little drizzle of salsa verde.)