Pour the oil, vinegar, orange juice, coconut sugar, whole grain mustard, garlic, salt, and chicken in a large plastic baggie and let it sit in your fridge overnight.
The next day, remove the chicken from the plastic baggie and discard the marinade.
Heat the grill on high for 5 minutes, then turn the heat down to medium.
Once the grill is heated, place the chicken on the grill and cook for 2 – 3 minutes per side.
In a small mason jar, or jar with a lid, place the dressing ingredients: orange juice, oil, agave nectar, apple cider vinegar, and garlic.
Toss the arugula with the dressing.
Top with sliced chicken, sliced oranges and grapefruit, crumbled gorgonzola, and chopped pistachios.