In a small bowl, mix together the soy sauce, brown sugar, diced onion, minced ginger, minced garlic, and crushed red pepper flakes.

In a skillet over medium-high heat, add the sesame oil and let it warm up before adding your lean ground beef. Cook until it's browned and well done.

Pour the prepared sauce mixture over the cooked ground beef in the skillet. Stir well to combine everything evenly. Allow it to simmer for a few minutes on low heat.

Scoop generous portions over fluffy white rice or your preferred base.