Prepare the tostada shells according to the linked recipe.
Warm up the cooked beans in a saucepan over medium heat. If using meat, warm it up separately.
Assemble the tostadas: Spread a layer of beans over each tostada shell. Add the cooked meat on top, if using.
Top with shredded lettuce or cabbage, diced tomatoes, and pickled onions, radishes, jalapenos, or fresnos.
Drizzle with salsa or pico de gallo, Mexican crema or sour cream, and sprinkle with queso fresco or shredded Monterey Jack cheese, if desired.
Serve immediately and enjoy!