Onion: Peel and finely dice. Put in a large bowl. Garlic: Peel and finely chop. Put in the large bowl as well. Ginger: Peel and finely chop like the garlic, put in the bowl. Chives: Chop and put in the bowl. Carrot: Peel and cut off the ends. Cut in half and cut into sticks. Cut into tiny cubes, or just chop with your knife until it's all really small. Put in the bowl. Napa cabbage: Thinly slice and then chop. Put in the bowl as well. Mushrooms: Chop into the same size as the carrots. Put into the bowl.
Getting rid of excess liquid
Now every vegetable is chopped and in the bowl, add a couple of pinches of salt and mix well with your hands. Sqeeze with your hands, and then let the vegetables sit in the bowl for about 15 minutes. Get 2 other bowls, you're going to grab a handful of the mixture and squeeze out as much liquid as you can into one of the bowls and then put the squeezed out veggies into the last bowl. Repeat with all of the vegetables.
Now that you have no excess liquid from the vegetables, you can start to add the soy sauce and the sesame oil. Mix well with a spoon and taste. You may want to add some white pepper but that is optional. Add in the corn starch as well, one tablespoon at a time. Overdoing it on the corn starch will result in a dry filling so you want the vegetables to be pretty dry but not too dry. I found that around 2 tablespoons was enough to achieve this.
Making the gyoza
First get yourself a bowl of water and a plate lined with baking paper to avoid the gyoza from sticking to the plate. Take 1 gyoza wrapper and add 1 tablespoon of filling in the middle. Brush the edge of the wrapper with water. There are 2 different ways I usually wrap my gyoza.
Rest the gyoza on your hand and place your index finger between the two edges. Make folds on 1 side of the gyoza, using your thumb, and pressing down so the edges stick together. Watch my video if this is unclear!
After filling the gyoza, push the edges together and fold using your index finger. Again, watch my video if this is unclear.
Heat up a pan on med-high heat with a little oil and place in a couple of gyoza. You're only going to crisp up one side. Sear one side for about 3 to 5 minutes or until the bottom is brown and crispy. Add the warm water to the pan and immediately cover with a lid. Steam for around 5 minutes. After 5 minutes, the water should be (almost) evaporated. Cook uncovered for another couple of minutes to crisp up the bottom again. Nutritional values are for 1 gyoza.