Preheat the grill or grill pan over medium-high heat.
In a bowl, mix olive oil, balsamic vinegar, Dijon mustard, honey, salt, and pepper to create a dressing.
Reserve 2 tablespoons of the dressing for tossing the salad; marinate the chicken breasts in the remaining dressing for at least 10 minutes.
Grill the marinated chicken for about 6-7 minutes on each side, or until the internal temperature reaches 165°F (75°C). Remove from grill and let rest for 5 minutes before slicing.
While the chicken is resting, prepare the salad by combining salad greens, cherry tomatoes, cucumber, bell pepper, avocado, and red onion in a large bowl.
Slice the grilled chicken and place it on top of the salad mixture.
Drizzle the reserved dressing over the salad and toss gently to combine.
Garnish with fresh herbs if desired, then serve immediately.