Combine Yogurt Sauce ingredients in small bowl; cover and refrigerate.
Combine oregano and garlic; press evenly onto beef Flat Iron Steaks. Heat large nonstick skillet over medium heat until hot. Place steaks in skillet; cook 11 to 14 minutes for medium rare (145°F) to medium (160°F) doneness, turning occasionally.
Carve steaks into thin slices; season with salt and pepper, as desired. Serve beef in pita pockets with tomatoes, onion and yogurt sauce.
Nutrition information per serving: 402 Calories; 117.9 kcal Calories from fat; 13.1 g Total Fat; 5.1 g Saturated Fat; 0.4 g Trans Fat; 1 g Polyunsaturated Fat; 5 g Monounsaturated Fat; 75 mg Cholesterol; 738 mg Sodium; 41 g Total Carbohydrate; 4 g Dietary Fiber; 31 g Protein; 4.6 mg Iron; 552 mg Potassium; 5.2 mg NE Niacin; 0.6 mg Vitamin B6; 5.4 mcg Vitamin B12; 9.4 mg Zinc; 63 mcg Selenium; 119.2 mg Choline;