Prepare the Vegetables: Cut the green onions, leek (optional), zucchini, jalapeno (optional), onion, and sweet potato into the specified shapes and sizes.
Mix the Batter: In a large bowl, mix together 3/4 cup flour, 1/2 teaspoon salt, and 3/4 cup water.
Combine Vegetables and Batter: Add the prepared vegetables to the batter and mix well.
Cook the Pancake: Heat 2 tablespoons of vegetable oil in a non-stick skillet over medium-high heat. Add the vegetable and batter mixture, spreading it evenly. Reduce heat to medium and cook until the bottom is golden brown, then flip and add another tablespoon of oil, cooking until the other side is also golden and crispy.
Prepare the Dipping Sauce: Mix 1 tablespoon soy sauce, 2 teaspoons vinegar, hot pepper flakes (optional), and sesame seeds in a small bowl.
Serve: Serve the vegetable pancake hot with the dipping sauce on the side.