Dice the onion and chop the Napa cabbage. If using leftover chicken or other protein, cut it into small pieces.
Whisk the eggs in a bowl and set aside.
Heat oil in a large pan or wok over medium-high heat and cook the chicken or other protein (if using) until heated through, then set it aside.
In the same pan, sauté the onion for 2-3 minutes until softened.
Add the Napa cabbage and peas, cooking for another 2-3 minutes until tender.
Push the vegetables to one side of the pan and add the leftover rice. Fry it for about 2 minutes, stirring occasionally.
Mix the rice with the vegetables, then season with soy sauce and chili flakes to taste.
Pour the whisked eggs directly into the rice and stir until cooked.
Garnish with chopped spring onions and sesame seeds before serving.