A good tostada should crunch at the first bite and still hold enough topping to feel like dinner. These pair sweet potato browned at the edges with warm black beans and a quick avocado-lime crema, so each tortilla has something crisp, creamy, and savory.
Roast the sweet potatoes
Heat the oven to 425°F. Peel 1 large sweet potato and cut it into ½-inch cubes, then toss with 1 tablespoon olive oil, ½ teaspoon ground cumin, ½ teaspoon smoked paprika, and a good pinch of salt.
Spread the cubes in one layer on a sheet pan and roast for 22 to 28 minutes, turning once, until tender inside and browned at the corners. Crowding the pan can make them steam, so use a second pan if the pieces are piled on top of one another.
Make crisp tortillas and crema
Brush 8 small corn tortillas lightly with oil and arrange them on a second baking sheet. Bake for 8 to 12 minutes, turning once, until crisp and dry to the touch; watch closely near the end, since thin tortillas can brown quickly.
For the crema, mash 1 ripe avocado with ⅓ cup plain yogurt, the juice of 1 lime, and a pinch of salt until mostly smooth. Warm 1 can of drained black beans in a saucepan with ¼ teaspoon cumin and a splash of water, stirring until hot and lightly saucy.
Layer while everything is warm
Spread each crisp tortilla with a spoonful of black beans, then add the roasted sweet potato and a drizzle of avocado crema. Finish with chopped cilantro, thinly sliced red onion, or a little crumbled cheese if you have them.
Serve the tostadas as soon as they’re assembled, while the tortillas still crackle beneath the toppings. For a relaxed dinner, bring the components to the table separately and let everyone build their own; keep extra lime wedges nearby for a brighter finish.