Heat olive oil or butter in a large skillet or pot over medium heat.
Add sliced onions and cook, stirring occasionally, until golden brown and caramelized, about 15–20 minutes.
Stir in minced garlic and thyme and cook for 1 more minute until fragrant.
Add ground beef to the pot, breaking it up as it cooks, until browned and cooked through.
Season with salt, pepper, and Worcestershire sauce.
Stir in the rice to combine evenly with the beef and onions.
Pour in beef broth and bring the mixture to a boil.
Reduce heat to low, cover, and simmer for 18–20 minutes or until rice is tender and liquid is absorbed.
Fluff the rice with a fork, then top with shredded cheese if using, allowing it to melt.
Garnish with fresh parsley and serve warm.