Step 1

Place steak in zippered plastic bag with 1/2 cup Mongolian Style BBQ sauce, press air out of bag and close. Refrigerate 4 hours, or overnight.

Step 2

Heat vegetable oil in large skillet over medium-high heat. Add garlic and cook until fragrant, about 30 seconds. Add mushrooms; cook and stir about 2 minutes. Add beef to skillet, leaving extra marinade in bag. Cook until almost browned, about 3 minutes.

Step 3

Add remaining 1/4 cup Mongolian Style BBQ sauce; cook until beef is just done and sauce is thickened, about 1 minute. Stir in green onions, remove from heat and serve.