1Remove fat from chicken. In 12-inch nonstick skillet, heat oil over medium heat. Cook chicken in oil about 12 minutes, turning once, until juice is no longer pink when centers of thickest pieces are cut. Remove chicken from skillet; keep warm.
2In same skillet, cook mushrooms, leek and garlic about 3 minutes, stirring frequently, until leek is tender. In medium bowl, mix remaining ingredients; stir into mushroom mixture. Heat to boiling, stirring occasionally. Boil and stir about 1 minute or until slightly thickened. Add chicken; heat through.