Cut steak crosswise into 1-inch-wide strips; cut each strip in half crosswise. Place the romaine in a large bowl.
Spray an unheated, heavy, 12-inch nonstick skillet with nonstick coating. Preheat over medium heat. Add mushrooms, sweet pepper and garlic to skillet; stir-fry for 2 to 3 minutes or until vegetables are crisp-tender. Remove vegetables; remove skillet from heat. Sprinkle vegetables with 1 teaspoon of the Italian seasoning, stirring to combine; set aside.
In the same skillet, heat oil over medium-high heat. Stir-fry beef strips, half at a time, in oil for 1 to 1-1/2 minutes. (Do not overcook.) Remove meat; sprinkle with the salt and set aside. Remove skillet from heat; add tomatoes, vinegar and the remianing Italian seasoning, stirring to combine. Return beef and veetables to skillet; stir to combine.
Spoon beef mixture and pan juices over romaine. Toss and serve immediately. Sprinkle each serving with freshly ground black pepper and Parmesan cheese, if desired.