1. In a bowl, make the dipping sauce by combining soy sauce, vinegar, hot pepper flakes (if using), and toasted sesame seeds. Mix well with a spoon and transfer it to a small bowl. Set aside.

2. In a separate bowl, combine green onion, leek (if using), zucchini, green chili pepper (if using), onion, sweet potato, all-purpose flour, salt, and 180 ml (¾ cup) water. Mix well with a wooden spoon to make the batter.

3. Heat a large non-stick skillet over medium-high heat. If your skillet is small, you can work in batches to make smaller pancakes.

4. Add about 2 tablespoons of vegetable oil to the skillet and swirl it around to coat the surface evenly. Add the batter to the skillet and spread it out evenly.

5. Reduce the heat to medium and place the sliced mushroom on top of the batter. Gently press them in with a wooden spoon or spatula.

6. Cook for 4 to 5 minutes until the bottom turns light golden brown and crispy. Grab the skillet handle and twirl it around to ensure even cooking underneath the pancake.

7. Flip the pancake or turn it over using a spatula.

8. Increase the heat to medium-high and add 1 to 2 tablespoons of vegetable oil along the edges of the pancake. Lift up one edge with a spatula and tilt the skillet so the oil flows underneath the pancake.

9. Cook for an additional 3 to 4 minutes until both sides turn light golden brown, occasionally pressing down with the spatula.

10. Flip the pancake over one more time and cook for another 2 minutes.

11. Transfer the vegetable pancake to a serving plate and cut it into wedges.

12. Serve the pancake hot with the prepared dipping sauce.

Note: The quantities provided are approximate and can be adjusted according to your preference. The calorie count may vary depending on the specific brands and ingredients used.