In a large pot of salted, boiling water, cook rice until tender. Drain, set aside, and keep warm.
In a food processor or blender, combine shallots, garlic, chopped cilantro, ginger, tamarind paste, anchovy, and brown sugar and puree until smooth.
In a soup pot, combine puree, cayenne, fish sauce, and clam juice and bring to a boil. Add fish and let simmer for 5 minutes. Add rice and simmer for 2 minutes. Remove soup from the heat and stir in lettuce, radishes, and snow peas. Ladle soup into bowls and serve sprinkled with scallions, cilantro leaves, and cucumber.
Recipe courtesy of Georgia Downard