Heat the oven to 350 degrees. In a 10-inch nonstick skillet, cook the ground beef over medium-high heat for 6 to 8 minutes or until thoroughly cooked, stirring occasionally to break up the beef. Stir in the chipotle chile, adobo sauce, taco sauce, beans, and salt. Cook the mixture for 3 minutes or until thoroughly heated. Meanwhile, heat the tostada shells in the oven as directed on the package. To serve, place the tostada shells on serving plates. Top the shells with the meat mixture, lettuce, tomato and dollop of sour cream.