Preheat oven to 325°F. Place brisket, fat side up, in foil-lined 13x9-inch baking pan. Mix hibiscus flowers and spices in small bowl. Reserve 2 tablespoons for the BBQ Sauce. Rub remaining spice mixture all over brisket. Add water to pan; cover tightly with foil.
Braise in oven 3 hours. Meanwhile, for the BBQ Sauce, heat oil in medium saucepan on medium heat. Add onion; cook and stir 4 minutes or until softened. Add sugar, tomato paste, water, vinegar and reserved spice mixture; mix well. Bring to boil. Reduce heat to medium-low; simmer 20 minutes or until thickened, stirring occasionally. Remove brisket from oven. Spoon 1 cup of the BBQ Sauce over brisket. Cover.
Braise in oven 1 hour longer or until brisket is tender. Transfer brisket to cutting board. Slice across the grain into 1/4-inch thick slices. Return brisket to pan. Spoon pan juices over brisket. Serve with remaining BBQ Sauce