Preheat the grill to medium-high heat.

Rub the flank steak with olive oil, salt, and black pepper.

Grill the steak for about 5-7 minutes on each side for medium-rare, or until desired doneness.

Remove from grill and let rest for 5 minutes before slicing.

In a small bowl, whisk together Dijon mustard, red wine vinegar, minced garlic, honey, salt, and black pepper.

Slowly drizzle in olive oil while whisking until emulsified.

In a large salad bowl, combine mixed greens, cherry tomatoes, cucumber, and red onion.

Slice the grilled steak against the grain and place on top of the salad.

Drizzle the vinaigrette over the salad and toss gently to combine.

Serve immediately.