in a heated wok add the pork and break apart well, stir fry with salt and pepper until beginning to brown, 3-4 minutes. If juices are forming at the bottom, spread the pork around the sides so it can evaporate off. You want the pork to get some crunchy maillard going on, steam is the enemy of that!
When the pork is nicely browning, add the green onion whites and the sauce, stir to combine with the pork
Combine the corn starch and water in a separate bowl, then stir into the sauce and stir fry for about a minute, just to get the sauce bubbling
Add the green onion greens, remove from heat and set aside to cool