Place Potatoes in microwave safe dish and cover with plastic wrap, venting one corner. Microwave on high for 7-9 minutes or until just tender, set aside.

Cut steak lengthwise into thirds, then crosswise into 1/4 inch thick slices. In a large skillet, heat 1 tablespoon of oil over medium-high heat until hot. Add 1/2 of the beef, cook and stir for 2-3 minutes or until browned. Using slotted spoon, remove to large bowl. Repeat with remaining oil and beef. 

Combine both batches of beef and Worcestershire sauce, toss to combine. 

Add Potatoes to skillet, cook and stir until most of the liquid is absorbed. Add beef, cheese and onions, mix lightly until cheese just melts. Season with salt and pepper as desired.

To serve, spoon 1/2 cup Potato mixture onto center of each tortilla. Fold bottom edge up over filling, fold right and left sides to center, overlapping the edges. Serve with steak sauce if desired.