1.Combine fish in medium bowl with juice, ginger and cumin. Cook fish in small baking-paper-lined steamer, over small saucepan of simmering water, about 10 minutes. Using two forks, flake fish.
2.Meanwhile, segment grapefruits over small bowl; reserve ⅓ cup of the juice for dressing. To make dressing; place reserved juice, vinegar and sugar in screw-top jar; shake well.
3.Divide spinach, sprouts, cucumber and grapefruit segments among serving plates; top with flaked salmon and dressing.