Heat the grill to medium for direct grilling. Slice the mangoes in 2 pieces from the pit. Score the flesh of the mangoes in a diamond pattern, taking care not to cut into the skin. Pop the flesh by holding the skin side and pushing up. Brush the flesh with the oil and grill, cut-side down, until slightly charred, about 1 minute.
Transfer the mangoes to a platter and immediately drizzle with the lime juice and sprinkle with the salt, chile powder and lime zest. Garnish with cilantro leaves if desired.