Preheat a gas or charcoal grill to medium-high heat. Combine the spinach and onions in a bowl and divide between two plates. Season the chicken with salt and pepper.
Spray the grill with cooking spray and add the chicken. Grill until cooked through, about 7-8 minutes per side. When chicken is almost done, add the pineapple slices to the grill and cook until charred. Allow both to cool slightly and then slice the chicken and chop the pineapple.
Combine the sesame oil, lime juice, pineapple juice, honey, cumin, and garlic in a jar and shake until well mixed. Toss with the salad and top with the chicken and pineapple. Top the salad with the chicken, pineapple, and toasted coconut before serving.