Preheat grill on high and set the grill rack 4 to 6 inches above the heat source.

Season chicken breasts with salt and pepper.

Coat chicken with olive oil cooking spray.

Grill chicken, turning once, until it reaches an internal temperature of 165°F, about 5 to 8 minutes per side.

Transfer chicken to a cutting board to rest.

Coat peach halves with olive oil cooking spray.

Place peaches skin side up on grill grates.

Grill peaches, turning once, until juicy but not mushy, about 3 to 5 minutes per side.

In a salad bowl, whisk together whole-grain mustard, white balsamic vinegar, extra-virgin olive oil, and 1 tablespoon of water to make the dressing.

Toss baby arugula with the dressing.

Divide the arugula among 4 plates.

Slice the grilled chicken and peaches.

Distribute the sliced chicken and peaches evenly among the plates.