Heat oil in stockpot over medium heat until hot. Place beef roast in stockpot; brown evenly. Remove roast from stockpot.

Add onions to stockpot; cook 8 to 10 minutes or until tender and lightly browned, stirring occasionally. Add water and au jus mix. Return roast to stockpot; bring to a boil. Reduce heat; cover tightly and simmer on range top or in preheated 325°F oven 2-1/2 to 3-1/4 hours or until roast is fork-tender.

Remove roast; keep cooking liquid warm. Carve roast across the grain into thin slices. Top rolls evenly with beef. Serve with au jus liquid in small bowls for dipping.

Slow Cooker Variation: Omit vegetable oil. Place onions in 3-1/2- to 5-1/2-quart slow cooker. Top with beef roast. Combine water and sauce mix; pour over roast. Cover and cook on HIGH 6 to 7 hours, or on LOW 10 to 11 hours, or until beef is fork-tender. (No stirring is necessary during cooking.) Proceed as directed in step 3.

Source: Recipe adapted from www.beefitswhatsfordinner.com