Slice the sayote and mix with salt and sugar. Let it rest for about 30 minutes. Mix every 5 - 10 minutes. A lot of water will be drawn out of the sayote. Don't throw this away as you'll use it later.
In another large bowl mix together the garlic, ginger, green onions, chili pepper flakes, and fish sauce. Use a glove or the chili pepper will burn your hand.
Add the sayote (but not the water) into the bowl of spicy mix. Mix until the spicy mix is well distributed. Add ½ c of the leftover water if you feel it needs more water to mix thoroughly. Add another ½ c if you think it needs more.Note: In this case, Mom actually used up all of the leftover water.
You can eat this right away, but it's best if you wait at least 2 days.