Combine olive oil, balsamic vinegar, lemon zest, lemon juice, oregano, garlic and red pepper in a small bowl.
Add lettuce, feta, mushrooms, onion, tomato and olives in a salad bowl.Toss salad with dressing.Season flank steak with your favorite grill seasoning. I love Martha Stewarts recipe.
Heat grill pan over medium heat. Spray with cooking spray.
Add steak and cook 4 8 minutes per side, depending on how thick and your desired doneness.