Heat 1 tablespoon olive oil in a large skillet over medium heat until it shimmers.

Add the sliced onion in an even layer. Cook, stirring occasionally, for 10 to 12 minutes until the onions are soft and golden brown. Lower the heat slightly if they start to brown too quickly.

Stir in the minced garlic and cook for 1 to 2 minutes until fragrant.

Add the ground beef to the skillet. Break it up with a spatula and cook until no pink remains.

Carefully drain excess fat into a heatproof container and discard. Return the skillet to the stove.

Stir in Worcestershire sauce and soy sauce. Add thyme if using. Season with salt and pepper and mix well.

Let the mixture simmer for 5 minutes so the flavors meld. Taste and adjust seasoning.

While the beef simmers, toast the hamburger buns lightly until golden.

Spoon the beef and onion mixture onto the bottom half of each bun. Sprinkle each with shredded Swiss cheese. Top with the bun crown.

Garnish with chopped parsley if you like, and serve right away.