Take the outer layers of your nappa cabbage off and set aside. Cut your cabbage into 4 quarters.
After you have cut the cabbage into quarters, cut the quarters in thin slices.
Place the cabbage in a bowl, and sprinkle the sea salt all over it. Massage the salt into the cabbage with your hands until it starts to soften a bit.
Cover the cabbage with cold water. Use enough water to JUST cover the cabbage. Place a plate and a heavy weight of some sort to hold it down on the cabbage.
Let it sit for at least an hour.
Mix together the ginger, garlic, sugar, and fish sauce until it forms a paste. Add in the chili powder. Set aside.
After the cabbage has sat for an hour, rinse it in a colander. Make sure to rinse it well. Let it drain for 10-20 minutes.
Cut up the carrots into matchstick pieces. Slice of your green onions. Put in a bowl.
Squeeze out the rest of the water from the cabbage and then add the cabbage to the bowl.
Add the paste. Mix together with GLOVED hands or a spoon or spatula. Make sure the vegetable mixture is completely covered in the paste.
After it is all mixed in, stuff it into a jar. Make sure to pound it down with every little bunch you put in the jar. Use a wooden spoon to do this. Make sure once your jar is full that the kimchi is completely submerged under the brine.
Take a cabbage leaf and fold it up. Put it in the top of the jar of kimchi to help weigh it down under the brine.
Put a lid on the kimchi and place it in a warm spot for 2-5 days. Check it everyday. Unscrew the lid each day to let the gases out and to make sure the kimchi is under the brine. If it isn't, push it down.
Once it has fermented to your liking, put it in the fridge and enjoy!