In a large mixing bowl, combine all-purpose flour and salt, creating a well in the center. Carefully pour in hot boiling water and mix until a shaggy dough forms. Knead the dough on a floured surface for about 10 minutes until smooth and elastic. Cover and let rest for 30 minutes.

While the dough rests, prepare the filling by wringing out excess moisture from the firm tofu. Heat oil in a skillet over medium heat and sauté the green beans for 1-2 minutes until tender yet crisp. Mix the sautéed green beans with tofu, carrot, cilantro, sesame oil, salt, and white pepper.

After resting, roll the dough into a log and cut into 10 equal pieces. Flatten each piece into a disk about 1/4 inch thick. Place a portion of the veggie mixture in the center, pleat and seal the edges tightly.

Heat a non-stick pan over medium heat with enough oil to coat the bottom. Slightly flatten each assembled bun and place them in the pan. Cook for about 4-5 minutes until the bottoms turn golden brown. Flip and add hot water until it reaches about 1/3 of the bun's height. Cover and steam for 3-5 minutes.

Remove the lid and let the buns cool slightly in the pan before transferring to a serving plate. Garnish with chopped green onions if desired. Serve warm with soy or spicy dipping sauce.