Caramelize onions in olive oil over medium-low heat for 15-20 minutes until golden.
Add ground beef, cook until browned.
Stir in garlic, Worcestershire sauce, soy sauce, thyme, salt, and pepper.
Simmer for 5-7 minutes until flavors meld.
Toast hamburger buns until golden.
Spoon beef mixture onto buns, top with Swiss cheese.
Optional: broil for 1-2 minutes until cheese melts.
Garnish with fresh parsley and serve immediately.
