Finely dice the onion and set it aside. Have the frozen mixed vegetables and day-old rice ready to go.
Heat a pan over medium-high heat with a bit of oil. Add the thinly sliced beef and cook until about 80% of the way through, then remove it from the pan and set aside.
In the same pan, add the onion, garlic, and ginger and stir until fragrant. Add the mixed vegetables and cook until the moisture has evaporated.
Return the beef to the pan along with the day-old rice, then add the light soy sauce, Worcestershire sauce, curry powder, sugar, and ketchup. Mix until the sauce has soaked into the rice grains and everything is evenly coated, then remove from the heat.
Transfer to a bowl and optionally garnish with scallions.
