In a small bowl, whisk together soy sauce, red chili flakes, oil, brown sugar, garlic and ginger. In a medium-sized bowl, add pork and pour half of the marinade over it, stirring to combine. In another medium-sized bowl, add onions and cabbage and pour remaining marinade over top. Let pork mixture and cabbage mixture stand 15 minutes at room temperature and or up to one day in the refrigerator.
In a large skillet over medium-high heat, add pork; breaking it up with the back of a spoon until brown and no pink remains, about 5 minutes. Transfer cooked pork to a bowl. In same skillet, add cabbage mixture with marinade and cook until onions are translucent and cabbage is tender and crisp, about 10 minutes. Return pork with any accumulated juices back to the skillet, tossing to combine. Cook for approximately 5 minutes until flavours are combined.
Divide rice into 4 small bowls. Top with pork mixture and serve immediately. Sprinkle with sesame seeds and green onions if desired.