Seed and coarsely chop jalapeño. Thickly slice onions. In a blender or food processor, whirl jalapeño, onions, romaine, coriander and garlic until puréed. Pour purée into a 4-cup (1-L) measuring cup, then add undiluted broth and some water, if necessary, to make 4 cups (1 L).
Heat oil in a large saucepan set over medium-high heat. Add rice. Stir until all grains are well coated with oil and shiny, from 1 to 2 minutes.
Stir in purée-broth mixture and salt. Bring to a boil over high heat. Then cover, reduce heat to low and simmer until rice is tender and liquid is absorbed, from 18 to 20 minutes. Let rice stand at least 5 minutes before serving. Fluff with a fork and serve with grilled fish or chicken. Excellent hot or at room temperature.