To make the meatballs, combine the beef, onion, breadcrumbs, soy sauce, salt, pepper & egg in a large mixing bowl and gently mix until well combined.
Form the mixture into 1 1/2” balls and place on a baking sheet.
Bake the meatballs at 400 degrees for 15-20 minutes, until browned and cooked through.
While the meatballs cook make the glaze.
Combine the garlic, ginger, gochujang, maple syrup, mirin, soy sauce, vinegar, brown sugar, sesame oil and water in a bowl and whisk until smooth.
Pour the glaze into a heavy skillet and simmer over medium-high heat until bubbling and sticky.
Add the meatballs into the pan with the glaze and toss well.
Serve on steamed rice, topped with green onion, cucumber, cilantro and sesame seeds.