Cut each chicken breast fillet into four to make 24 cubes. Place in a bowl with all remaining ingredients except the melted butter. Let marinate 2 hours, turning occasionally. Soak wooden skewers in cold water.
Preheat the barbecue and thread the pieces onto 4-6 skewers. Brush the BBQ grill lightly with oil and cook the chicken, turning as necessary, about 20 minutes. Serve with melted butter poured over.