The horseradish makes this a perfect accompaniment for roast beef or ham.
Soften the gelatin in cold water in a medium-size saucepan; stir in the instant onion, salt and sugar. Heat just to boiling. Remove from the heat, stir to dissolve the gelatin completely, and then stir in the grated cucumber, sour cream, horseradish and vinegar.
Pour into a mold; chill 4 hours or until firm. Unmold and garnish with cherry tomatoes and ripe olives.