In a large skillet over medium-high heat, add about a tbsp of neutral oil. Onced heated add the minced garlic and ginger and cook until fragrant, about 30 seconds.
Add the chopped cabbage and cook until softened, about 3-5 minutes. Remove from heat and let cool.
In a large mixing bowl, add ground pork, green onions, soy sauce, corn starch, sesame oil, and optional umami seasoning. Using your hands, mix until combined.
Add the cooled cabbage to the sausage mixture and mix well.
Lay out a gyoza wrapper on a clean work surface. Spoon 1-2 tablespoons of the filling into the center of the wrapper.
Dip your finger into a bowl of water and run it along the edges of the wrapper.
Fold the wrapper in half to enclose the filling and pleat the edges together to seal the dumpling.
Repeat with the remaining wrappers and filling.
In a large non-stick skillet, heat a 1-2 tablespoons of oil over medium heat. Add the gyoza in a single layer and fry until the bottoms are golden brown, about 2-3 minutes.
Pour in enough water to the skillet to come about 1/4 inch up the sides. Cover the skillet with a tight-fitting lid and let the gyoza steam for 3-5 minutes, or until most of the water has evaporated.
Remove the lid and let the gyoza cook until the rest of the water has evaporated.
Serve hot with the dipping sauce and garnish with chopped scallions.