Coat a large nonstick skillet with cooking spray; place over medium-high heat until hot. Add onion; cook 5 minutes or until lightly browned. Add chicken; sauté each side 3 minutes or until browned.
Combine wine and next 8 ingredients (wine through black pepper) in a medium bowl; stir well. Add wine mixture to chicken mixture; cover, reduce heat, and simmer 20 minutes. Serve with Pepper-Spiked Polenta. Garnish with tarragon sprigs, if desired.