Add sweet potato and 2 tsp olive oil to a skillet. Cook stirring occasionally until the sweet potato starts to caramelize and gets tender. Stir in red pepper flake and chili powder. Coarsely mash the sweet potato with a fork or the back of a spoon.
Meanwhile combine the black beans, garlic, salt, pepper, cumin, lime juice, and remaining olive oil, stirring to coat.
Top each tostada shell with sweet potato mixture, salsa, black bean mixture, queso fresco and minced cilantro. Serve immediately.
Recipe by Alison's Allspice at https://www.alisonsallspice.com/sweet-potato-black-bean-tostadas/