Heat the sesame oil in a large skillet or braiser over medium heat. Add the onion and cook for 3 to 4 minutes, until softened.
Add the garlic and ginger and cook for 30 seconds, until fragrant.
Add the ground beef, breaking it apart with a wooden spoon, and cook until browned, 6 to 8 minutes.
Drain any excess fat if needed.
Stir in the coconut aminos, beef broth, rice vinegar, and red pepper flakes.
Bring to a gentle simmer, then reduce the heat to low and cover partially.
Braise for 20 minutes, stirring occasionally, until the sauce has reduced and thickened slightly.
Season with salt and pepper to taste.
Garnish with sliced green onions and sesame seeds before serving.