Heat oven to 350°F. Cut beef steak lengthwise in half, then crosswise into 1/8-inch thick strips. Combine beef and 1/3 cup dressing in medium bowl; toss to coat. Cover and marinate in refrigerator 30 minutes.
Place pita breads slightly overlapping on metal baking sheet. Sprinkle 2 tablespoons cheese on each pita. Bake in 350°F oven 10 to 12 minutes or until pitas are toasted and cheese is melted.
Meanwhile, remove beef from marinade, draining well; discard marinade. Heat large nonstick skillet over medium-high heat until hot. Add 1/2 of beef; stir-fry 1 to 2 minutes or until outside surface of beef is no longer pink. Remove from skillet. Repeat with remaining beef.
Toss lettuce, tomatoes and remaining 1/2 cup cheese in large bowl. Add beef and remaining 1/3 cup dressing; toss to coat evenly. Season with salt and pepper. Divide beef mixture evenly over pitas. Serve immediately.
Nutrition information per serving: 432 Calories; 135 kcal Calories from fat; 15 g Total Fat; 5 g Saturated Fat; 2 g Monounsaturated Fat; 61 mg Cholesterol; 915 mg Sodium; 35 g Total Carbohydrate; 6.8 g Dietary Fiber; 40 g Protein; 4.2 mg Iron; 8 mg Niacin; 0.7 mg Vitamin B6; 1.5 mcg Vitamin B12; 5.1 mg Zinc; 30.8 mcg Selenium;