Combine first 6 ingredients in a blender or food processor; process until blended.
Place cilantro mixture and chicken pieces in a large zip-top plastic bag. Seal bag, and shake to coat chicken. Marinate in refrigerator 8 hours.
Remove chicken from marinade, discarding marinade. Place chicken on grill rack coated with cooking spray; grill 2 to 3 minutes on each side or until done.
Chop chicken and divide chicken evenly among tortillas. Top each with 2 tablespoons shredded lettuce, 2 tablespoons chopped tomatoes, 1 tablespoon cheese, and 1 tablespoon sour cream. Fold bottom half of each tortilla over filling.