In a medium bowl, whisk together soy sauce, brown sugar, sesame oil, rice vinegar, and gochujang until combined. Stir in minced garlic and grated ginger.
In a large bowl, mix the ground beef with the marinade and sliced yellow onion. Cover and refrigerate for at least 30 minutes.
Heat a skillet over medium-high heat. Add the marinated beef in a single layer and cook for 8-10 minutes, breaking it apart as it cooks until fully browned.
Serve over cooked rice or in lettuce wraps garnished with sliced green onions and sesame seeds.