Preheat your grill to medium-high. Divide and thread the chicken, mango and onion onto the skewers. Brush lightly with the oil; season with salt and pepper. Lightly oil the bars of the grill. Grill kebabs 7 to 8 minutes, turning occasionally, or until the chicken is cooked.
While the kebabs cook, place the plum, chili and soy sauces, lime juice and ginger in a small pot and bring to a simmer. Remove from the heat and cover.
When cooked, set 1 kebab on each of 4 plates, generously brush with the plum sauce mixture, sprinkle with green onion and serve.
Note: Wooden skewers must be soaked in cold water for at least one hour before using.