In a large bowl, combine the pork, onion, ginger, bell pepper and carrot. In a small bowl, dilute the curry paste with 1 tablespoon water and combine with the salsa. Pour the curry mixture into the pork mixture and blend thoroughly.
Line racks of a bamboo steamer with the lettuce leaves to prevent sticking. To form the dumplings, place 1 teaspoon of the filling on each won-ton wrapper. Moisten the edges with water; fold the won-ton wrapper over the filling to form a half moon. Moisten the ends and turn up to close. Set the dumplings on the lettuce leaves, not allowing the dumplings to touch.
When the racks are full, set the steamer over boiling water in a wok and steam until the dumplings are cooked through and firm, 12 to 15 minutes. Let the dumplings rest a few minutes before serving with Mango Relish.
Note: Dumplings can be made 2 weeks ahead, covered tightly and frozen. Do not thaw before steaming.