Mix ground chicken, egg, panko, grated onion, garlic, Worcestershire sauce, and seasonings in a bowl.
Shape into 6 oval patties with a slight indent in the center. Chill for 10 minutes if possible.
Heat oil in a skillet over medium heat. Sear patties for 4-5 minutes per side until golden brown.
Remove and keep warm.
In the same pan, melt butter and cook mushrooms and onions until soft and browned.
Sprinkle flour over mushrooms, stir, then gradually add broth, cream, soy sauce, and Dijon mustard. Simmer until thick.
Return patties to the pan, coat with gravy, and simmer for 2-3 minutes. Adjust seasoning if needed.
Garnish with fresh thyme and black pepper.
Serve warm.