1. Combine first 9 ingredients in a large saucepan; bring to a boil. Cover, reduce heat, and simmer 15 minutes. Stir in tea leaves; simmer 2 minutes. Strain mixture through a sieve into a large bowl; discard solids. Stir in ice; chill.
2. Add shrimp to water mixture; chill 20 minutes.
3. Prepare grill.
4. Remove the shrimp from bowl; discard liquid. Pat the shrimp dry with paper towels. Thread 4 shrimp and 2 mango pieces alternately onto each of 8 (12-inch) skewers.
5. Place the skewers on a grill rack coated with cooking spray. Grill for 2 minutes on each side or until the shrimp are done. Sprinkle with sliced green onions. Serve with flatbread.
Note: As pictured on the cover, you can use smaller skewers. Simply thread two shrimp alternately with two mango chunks, and serve guests two skewers each. You'll need to purchase an extra mango (which minimally increases the calories per serving) if you opt for this presentation.