Fill a bowl with hot water. Soak one rice paper until it becomes soft, about 5 seconds.
Lay out the rice paper on a cutting board. Layer 2 oz tuna, mango, avocado, cucumber, bell pepper and scallions in a tight line in the center.
Tightly roll the end of the wrapper over the filling, then tightly tuck in each side before finishing rolling. The tighter the roll, the better!
Repeat for remaining wrappers. Place in the refrigerator to cool before serving.
For the sauce, bring all ingredients to a boil. Let reduce by about half, then cool before serving.
When both items have cooled, serve the summer rolls with the coconut-ginger dipping sauce.