Preheat the grill to medium-high heat.
Season the chicken breasts with salt and pepper.
Grill the chicken for 6-7 minutes per side or until fully cooked.
While the chicken is grilling, prepare the blackberry balsamic dressing.
In a bowl, combine mixed greens, blackberries, walnuts, and feta.
Once the chicken is grilled, let it rest for 5 minutes before slicing.
Slice the grilled chicken and add it to the salad bowl.
Drizzle the blackberry balsamic dressing over the salad and toss gently to combine.
Serve the salad immediately for the best flavor and texture.