Begin by whisking together your dressing. Combine oil, vinegar, lemon, mustard, 2 tbsp syrup, and salt in a tupperware bowl with lid and shake to combine.
Use about half of the dressing (1/4 cup -1/3 cup) as your marinade for the chicken. Place in a large ziploc bag and mix to coat the chicken. Let marinate for 15-30 minutes.
Prepare your grill.
Prepare your peaches: Cut each peach in half and remove the pit. Brush both sides of the peaches with remaining maple syrup.
Grill chicken and peaches. About 6-8 minutes per side for chicken until it is no longer pink, and about 5 minutes each side for the peaches. Remove, and dice peaches into small chunks and chicken into slices.
Place greens or pasta in a large bowl. Add red onion, peaches, and chicken and toss. Top with pecans, goat cheese (if using), and drizzle the dressing on top.
Serve immediately.