Cut beef Brisket Flat Half into 3 to 4 pieces. Heat oil in stockpot over medium heat until hot. Place beef brisket in stockpot; brown pieces evenly. Remove brisket from stockpot; set aside.
Add onions to stockpot; cook on low heat 18 to 22 minutes until lightly caramelized, stirring occasionally. Add broth, soy sauce, soup mix and garlic. Return brisket to stockpot; bring to a boil. Reduce heat; cover tightly and simmer 2-1/2 to 3 hours or until brisket is fork-tender.
Remove brisket; keep warm. Skim fat from cooking liquid. Carve brisket against the grain into very thin slices. Divide brisket evenly among rolls and top with prepared onions. Top with cheese, as desired. Close sandwiches. Cook's Tip: After carving, beef can be returned to cooking liquid and kept warm over low heat until ready to serve, if desired.
