Lemony Shrimp Dumplings

Name: Lemony Shrimp Dumplings
Ingredients: 3 tablespoons soy sauce; 3 tablespoons water; 2 tablespoons fresh lemon juice; 1 tablespoon Asian fish sauce; 1 scallion, thinly sliced; 1 1/2 pounds medium shrimp, shelled and deveined; 1 1/2 tablespoons cornstarch, plus more for dusting; 2 tablespoons soy sauce; 1 tablespoon fresh lemon juice; 1 large egg, beaten; 1 teaspoon finely grated lemon zest; 1 teaspoon kosher salt; 1/4 teaspoon freshly ground pepper; 1/2 cup diced, peeled jicama (1/4-inch); 2 scallions, thinly sliced; 45 gyoza wrappers (see Note); Green leaf lettuce leaves, for steaming