If using wooden skewers, soak them in water for at least thirty minutes. Skip this step if using metal skewers. Puree olive oil, pineapple, salt, pepper, ginger, garlic, and vinegar in a food processor until smooth. Pour mixture over chicken in a large bowl, cover, and refrigerate for thirty minutes. Alternately add chicken, bell pepper, and onion pieces on skewers (4 of each on each skewer). Cook on the grill or on the top rack of a 450 F oven on a foil-lined baking sheet for 20-30 minutes, flipping halfway through.