In a large bowl, whisk together the olive oil, lime juice, chili powder, cayenne, salt and sugar. Add the chicken and mangoes and stir gently to coat with the marinade. Cover and refrigerate for 2 to 4 hours.
Prepare a hot fire in a grill.
Remove the chicken and mangoes from the marinade and thread onto wood skewers, alternating the pieces and dividing them evenly.
Arrange the skewers on the grill and cook, turning once, until the chicken is nicely charred and cooked through, 6 to 10 minutes. Transfer the skewers to a warmed platter and serve immediately.