3/4 pound (1 1/2 cups) dried black beans, picked over
12 cups water
6 ounces (about 1 link) Mexican-style chorizo, casing removed and crumbled
1 stalk fennel, chopped
1 medium onion, chopped
3 chipotle chiles in adobo, chopped
4 teaspoons salt, or more to taste
1/2 teaspoon freshly ground black pepper
12 medium shrimp, peeled and deveined if necessary
5 corn tostadas, broken up or a handful of corn tortilla chips
1/2 cup crumbled queso fresco or cheddar cheese