01 - Preheat a grill pan or skillet over medium-high heat. Rub the chicken breasts with olive oil, salt, and black pepper on all sides.
02 - Cook the chicken for 6 to 7 minutes per side, or until golden and cooked through to an internal temperature of 165°F. Transfer to a plate and let rest for 5 minutes before slicing thinly against the grain.
03 - While the chicken rests, arrange the mixed salad greens on a large serving platter or in individual bowls. Top with halved cherry tomatoes, sliced cucumber, thinly sliced red onion, and sliced avocado.
04 - In a small mixing bowl, whisk together the mayonnaise, Dijon mustard, honey, fresh lemon juice, and Greek yogurt if using. Season with salt and pepper to taste. Adjust consistency with a splash of water if needed.
05 - Arrange the sliced chicken over the salad. Drizzle generously with the creamy honey mustard dressing. Toss gently to combine, or serve the dressing on the side.