In a large bowl, combine the onion, garlic, thyme and 1/2 cup cheese. Crumble beef over mixture and mix well. Shape into two oval patties.
In a large skillet, cook burgers over medium heat for 5-6 minutes on each side or until meat is no longer pink. Meanwhile, prepare Texas toast according to package directions.
Drain burgers; set aside and keep warm. Add the tomato sauce, brown sugar, Worcestershire sauce and steak sauce to the skillet. Bring to a boil; cook and stir for 1-2 minutes or until slightly thickened. Return burgers to skillet; turn to coat. Sprinkle with remaining cheese. Serve burgers on toast.