Preheat oven to 350°F. Rub brisket all over with Creole Seasoning. (If desired, refrigerate brisket 1 hour or overnight for extra flavor).
Heat oil in large deep ovenproof skillet or Dutch oven on medium-high heat. Add brisket; cook 6 minutes or until browned on all sides. Remove brisket; set aside. Add water to skillet, stirring to scrape up browned bits. Return brisket to skillet. Add onions and garlic; cover
Bake 2 1/2 hours or until brisket is fork tender. Remove brisket to cutting board. Reserve onions and liquid in medium bowl.
Melt butter in same skillet on medium heat. Gradually add flour, stirring with wire whisk until well blended. Cook 1 to 2 minutes or until bubbly and lightly browned. Add onions and liquid to skillet; bring to boil. Reduce heat to low; simmer 3 minutes or until gravy is thickened. Slice brisket; return to skillet. Simmer 5 minutes or until heated through