Preheat your oven to 400F and spill the diced sweet potato onto a large baking sheet. Drizzle with 3 teaspoons of olive oil and season with ¼ teaspoon each of sea salt and black pepper. Toss to coat. Roast the sweet potatoes for 20 minutes, shaking the pan halfway through, until tender. Transfer the sweet potatoes to a bowl and set aside. Leave your oven on.

Meanwhile, drain the black beans and reserve the liquid in a small bowl. Rinse the black beans and transfer them to a small saucepan or skillet and season with cumin, chili powder, ½ teaspoon of sea salt, and ¼ cup of the liquid from the can. Turn the heat to low and use a fork to stir and smash the black beans until heated through, about 3 minutes. Transfer the black beans to a bowl and set aside.

To make the tostadas, lightly brush both sides of the tortillas with olive oil and place them in a single layer over a few baking sheets. Bake for 8 minutes, flipping the tortillas halfway through. Remove the tortillas from the oven and allow them to cool.

Wipe out the skillet or saucepan you used to heat the black beans. Warm the remaining teaspoon of olive oil over medium-low heat. Add the garlic and chipotle peppers and sauté until lightly golden and fragrant, about a minute. Stir in the roasted sweet potato and cook until heated through, about 2 minutes. If you like spicy food, add some of the adobo sauce from the chiles to the pan one teaspoon at a time, tasting as you go (I added a tablespoon).

To serve, spread each tostada with about ¼ cup of black beans. Top with a scoop of sweet potato and chipotle peppers, sliced avocado, cabbage, and cilantro. Garnish each plate with a lime wedge and serve warm.