In a medium bowl, whisk together mango juice, pineapple juice, olive oil, honey, lemon juice, Dijon mustard, salt, pepper, and cayenne.
Place the chicken in a large zip-top bag and pour the marinade over it. Seal and refrigerate for at least 2 to 4 hours, or overnight.
Preheat grill to medium-high heat and oil the grates.
Grill the chicken for 5 to 7 minutes on each side, or until internal temperature reaches 165°F and the chicken is cooked through.
While the chicken is grilling, optionally grill the pineapple and mango pieces for 2–3 minutes per side until slightly charred.
Let the chicken rest for a few minutes, then garnish with grilled fruit and fresh herbs before serving.