Stack beef steaks; cut lengthwise in half and then crosswise into 1-inch wide strips. Set aside.
In a large nonstick skillet, heat oil over medium-high heat until hot. Add onion; cook and stir 3 minutes or until lightly browned. Remove from skillet; keep warm.
In same skillet, add beef, half at a time, and stir-fry for 1 minute or until outside surface is no longer pink. (Do not overcook.) Stir in onion and barbecue sauce; heat through, stirring occasionally.
Spoon equal amount of beef mixture on bottom half of each roll; close with top half of roll.