
Heat the olive oil in a large skillet over medium heat. Add the onions and sauté until soft and translucent, about 5 minutes.
Stir in chipotle peppers and adobo sauce and cook for 2 minutes.
Add the can of black beans along with their liquid, the salt, garlic powder, chili powder, and cumin. Stir and continue simmering for an additional 3-4 minutes, then stir in the broth until well combined and bubbling.
Using a hand masher or immersion blender, mash the black bean mixture until it reaches your desired consistency. For a super smooth consistency, transfer the black bean mixture into a blender or food processor and blend until smooth.
Assemble and serve the tostadas by spreading a heaping 1-2 tablespoons of the black bean mixture onto your tostada shell. Sprinkle with shredded cheese or queso fresco and top with chopped cilantro, shredded lettuce, diced tomatoes, Mexican crema, and your favorite salsa.