1. In a large soup pot, heat the oil over moderate heat, tipping the pot to coat the bottom evenly. Add the onions and garlic and cook, stirring, for 4 or 5 minutes, or until the onions are soft and transparent but not brown.
2. Add the tomatoes, oregano, bay leaf, salt and a few grindings of black pepper, and cook, stirring, for 5 minutes. Add the potatoes and water, cover, and cook over moderate heat for 20 minutes.
3. Then drop in the fish and coriander, stir once or twice, recover the pot, and cook for 10 minutes longer, or until the fish is firm and opaque and the potato is tender when pierced with the tip of a sharp knife.
4. To serve, ladle the soup into a heated tureen or large serving bowl. Sprinkle parsley on top of it.
NOTE: Bass has been substituted for the congrio fish of Chile, a variety not available in other country.
