Preheat the oven to 425°F (220°C).

In a large bowl, toss the diced sweet potatoes with olive oil, chili powder, cumin, paprika, salt, and pepper. Spread them out in a single layer on a baking sheet and roast for 25-30 minutes, or until tender and golden brown.

In a medium saucepan, heat the black beans over medium heat until heated through. Mash some of the beans with a fork to thicken the mixture.

In a small bowl, combine the diced red onion, corn kernels, cherry tomatoes, avocado, and cilantro. Season with salt and pepper to taste.

To assemble the tostadas, spread a layer of mashed black beans onto each tostada shell. Top with the roasted sweet potatoes and the corn and avocado salsa.

Serve the tostadas with optional toppings such as salsa, sour cream, and lime wedges.

Enjoy!