Cook lobster tails in boiling water 6-8 minutes or until done; drain. Rinse with cold water. Split and clean tails. Cut lobster meat into bite-sized pieces. Combine lobster, grapefruit sections and orange sections. Combine yogurt, juices and rinds with white pepper in a small bowl; stir with a wire whisk until well blended. Pour over lobster mix. Arrange spinach on individual serving plates. Top each serving with 1 cup of the lobster mix. Sprinkle with chives. Garnish with curled orange rind if desired.