MELT butter in large skillet on medium-high heat. Add chicken; cook 5 min. on each side or until golden brown on both sides.
ADD onions and garlic; cook 5 min. or until tender, stirring occasionally. Reduce heat to medium; cover. Cook an additional 20 min. or until chicken is cooked through (180°F). Remove chicken to platter; cover to keep warm.
STIR sour cream, chipotle peppers and olives into skillet. Cook, uncovered, 10 min. or until heated through, stirring occasionally. Pour sauce over chicken; sprinkle with the parsley.