In a small bowl, combine cornstarch and the 1 tablespoon water, stirring until smooth; set aside.
In a medium saucepan, combine the 1-1/4 cups water, orange juice concentrate, honey, and salt. Bring to a gentle boil over medium to medium-high heat, stirring frequently. Whisk in cornstarch mixture. Return to boiling; reduce heat. Cook and stir until thickened and bubbly. Cook and stir for 2 minutes more.
Stir in mandarin oranges and ginger; cool. Cover and chill for 2 to 24 hours. Serve over ice cream. If desired, sprinkle each serving with almonds.