In a medium bowl, mix the flour and salt. Pour the boiling water in gradually, stirring continuously with a fork to combine.

Knead the mixture with your hands until a smooth dough forms. Flatten the dough slightly, drizzle olive oil over it, and press and fold the dough to incorporate the oil. Shape it back into a ball, cover the bowl with plastic wrap, and let the dough rest for 1 hour.

Once rested, roll the dough out on a clean, flat surface to a thickness of 1/8 inch. Use a 3-inch round cookie cutter to cut out circles for the dumplings.

In a mixing bowl, stir together the hoisin sauce and cornstarch until smooth. Add the bok choy, shredded carrot, green onion, cilantro, and salt. Mix thoroughly to combine. Add the ground beef and blend well. Use a small ice cream scoop or your hands to shape the mixture into approximately 30 small meatballs.

Place a meatball in the center of a dough circle. Fold the edges of the dough up around the filling, crimping them together on one side. Turn the dumpling and crimp the edges on the other side, ensuring the filling is sealed completely. Gently flatten the base of the dumpling for stability. Repeat with the remaining dough and filling.

Line a bamboo steamer with cabbage leaves to prevent sticking. Arrange the dumplings in the steamer, ensuring they do not touch each other.

In a large pot or Dutch oven, bring water to a boil. Place the bamboo steamer over the boiling water, ensuring the dumplings are not in contact with the water. Cover the steamer and let the dumplings cook for 16–18 minutes.

Serve the dumplings warm with the soy dipping sauce.

Combine the rice vinegar and soy sauce in a small bowl. Garnish with chopped green onions if desired, and serve alongside the dumplings in individual dipping bowls.