Cut off 1/4-inch from blossom end (opposite stem end) of each tomato and with a 1/4-teaspoon measure carefully scoop out seeds. Wearing rubber gloves, seed and mince jalapeño.
In a small saucepan sprinkle gelatin over vegetable-juice cocktail or tomato juice and let stand 1 minute to soften. Heat mixture over moderately low heat, stirring, until gelatin is dissolved. Remove pan from heat and stir in jalapeño and all remaining ingredients except tomatoes. Cool filling slightly.
Using a small spoon and holding each tomato over saucepan, spoon filling into tomatoes, arranging tomatoes on a platter as filled. Chill tomatoes, covered, 4 hours, or until filling is set, up to 1 day. Garnish each tomato with a coriander leaf.