Sour Fish Soup With Tamarind

Name: Sour Fish Soup With Tamarind
Ingredients: 1 tablespoon oil; 1 small yellow onion, thinly sliced; 3/4 teaspoon salt; 1 1/2 teaspoons sugar; 1 1/2 tablespoons Vietnamese fish sauce; 1/4 cup tamarind liquid; 3/4 pound catfish fillet, cut into 1-inch pieces; 1 cup bite-sized chunks fresh or frozen pineapple, not canned (optional); 10 to 12 (about 1/3 pound) okra, stemmed and cut into 1-inch pieces; 1/2 pound tomatoes, cored, halved horizontally, seeded and cut into wedges; 2 cups (about 1/3 pound) bean sprouts; 1 teaspoon ground cumin; 5 or 6 sprigs cilantro, coarsely chopped