Place carrot, edamame, egg white, ginger, sesame oil, scallion, salt, soy sauce, rice vinegar, lemon juice, and Sriracha sauce, if using, in the bowl of a food processor; process until smooth.
Place 1 dumpling wrapper on work surface and top with 1 teaspoon filling. Brush edges with water and press to seal, forming a half moon shape. Keep wrappers covered with a damp towel to avoid drying out. Repeat process until all wrappers have been filled. Place dumplings on a baking sheet dusted with cornstarch until ready to steam.
Fill a large saucepan or wok with 2 cups water; bring to a boil. Place cabbage leaves or parchment round in bottom of bamboo steamer. Place dumplings in steamer, working in batches if necessary, cover and steam until wrappers have softened and filling is cooked through, about 8 minutes.