Prepare the filling: In a large bowl, combine ground pork, cabbage, green onions, garlic, ginger, soy sauce, sake, sesame oil, sugar, salt, and black pepper. Mix well until sticky.

Fill the wrappers: Place a teaspoon of filling in the center of each gyoza wrapper. Wet the edges with water, fold in half, and pleat the edges to seal tightly.

Heat a large non-stick pan over medium heat. Add 1 tbsp vegetable oil and arrange gyoza in a circular pattern, flat side down. Cook until bottoms are golden brown (about 2-3 minutes).

Add water: Pour 1/2 cup water into the pan (it will sizzle), then immediately cover with a lid. Steam for 5-6 minutes until most water evaporates.

Crisp the bottoms: Uncover and cook for another 1-2 minutes until bottoms are crispy again and any remaining water evaporates.

Serve: Use a spatula to transfer gyoza to a plate, crispy side up. Serve immediately with dipping sauce made of soy sauce, rice vinegar, and chili oil to taste.