Preheat grill to medium heat.
In a small bowl or cup, combine taco seasoning mix and oregano. Brush chicken with oil and sprinkle with taco seasoning mixture.
Grill chicken, covered, for 10 to 15 minutes or until cooked through, turning once.
Meanwhile, in a small microwavable bowl, combine barbecue sauce, chili sauce and cumin; cover and microwave on HIGH for 30 to 60 seconds or until hot.
Serve sauce over chicken.