• Step 1: Season the flank steak with salt and pepper. Heat a grill or grill pan over high heat and cook the steak for 3-4 minutes per side, or until it reaches your desired level of doneness. Let the steak rest for 5 minutes, then slice it against the grain into thin strips.
• Step 2: In a small bowl, whisk together the balsamic vinegar, Dijon mustard, olive oil, and minced garlic. Season with salt and pepper to taste.
• Step 3: In a large salad bowl, combine the mixed greens, cherry tomatoes, and sliced cucumber. Drizzle the balsamic vinaigrette over the salad and toss to coat.
• Step 4: Top the salad with the sliced steak and crumbled feta cheese. Serve immediately.