Heat the vegetable oil in a large skillet over medium heat.
Add the chopped yellow onion and minced garlic and sauté until the onion is translucent, about 2–3 minutes.
Add the ground beef and cook over medium heat, breaking it up with a wooden spoon, until no pink remains and it is browned.
In a measuring cup, whisk together the soy sauce, packed brown sugar, sesame oil, crushed red pepper flakes, ground black pepper, and ground ginger.
Pour the sauce over the cooked beef, stir well, and scrape any browned bits from the bottom of the pan into the sauce.
Cover the skillet and simmer over medium-low heat for 5 minutes to allow flavors to meld.
Serve the Korean beef over rice and garnish as desired.