In a large skillet set over medium heat, cook the chorizo, crumbling it with a wooden spoon, about 5-6 minutes.
While the chorizo is cooking, make the white sauce. In a small bowl or small food processor combine all ingredients and blend until smooth. Add milk, a little at a time, until desired consistency is achieved.
When the chorizo is fully cooked, add the refried beans to the skillet, mixing with the chorizo until fully combined and warmed through.
Spread the warm meat and bean mixture onto the tostada shells. Sprinkle with cotija cheese, iceberg lettuce, pico de gallo, guacamole and more cotija.
Drizzle the finished tostada with desired amount white sauce, a squeeze of lime and hot sauce.