Peach Balsamic Grilled Chicken

4 boneless skinless chicken breasts (about 2 lb. total)
Kosher salt
Freshly ground black pepper
Juice of 1 lemon
4 tbsp. balsamic vinegar
2 tbsp. peach preserves
1 tbsp. Dijon mustard
1/4 tsp. cayenne pepper
4 tbsp. extra-virgin olive oil, divided
4 ripe peaches, pitted and quartered
Chopped fresh basil, for serving

Season chicken on both sides with salt and black pepper. In a large bowl, combine lemon juice, vinegar, peach preserves, mustard, cayenne, and 3 tablespoons oil. Add chicken and turn to coat. Cover and let marinate at room temperature at least 30 minutes or up to 2 hours in the refrigerator.
Step
Prepare a grill for medium-high heat; preheat 5 minutes. Grill chicken, turning halfway through, until charred and an instant-read thermometer inserted into thickest part registers 165°, about 6 minutes per side. Transfer to a platter.

Reduce grill to medium heat. Brush cut sides of peaches with remaining 1 tablespoon oil. Grill until charred, 3 to 4 minutes per side.