In a large skillet, heat the olive oil over medium heat. Add the diced onion and cook for about 3-4 minutes until softened.
Add the minced garlic and cook for an additional 1 minute until fragrant.
Increase the heat to medium-high and add the ground beef. Cook until browned, breaking it apart with a spatula, about 5-7 minutes. Drain excess fat if necessary.
Stir in the Brussels sprouts, salt, black pepper, smoked paprika, soy sauce, balsamic vinegar, and beef broth.
Cover the skillet and reduce the heat to medium. Cook for 8-10 minutes, stirring occasionally, until the Brussels sprouts are tender.
If using, sprinkle the red pepper flakes over the mixture for added heat. Stir well and cook for an additional 1-2 minutes.
Serve hot, garnished with fresh herbs if desired.