Drain pears,reserving 3/4 cup liquid; set aside. In a large skillet, heat oil over medium-high heat until hot; cook chicken breasts until brown on both sides. Remove and set aside. Add onion and garlic to skillet; cook and stir 3 to 5 minutes or until onion is crisp-tender.
In small bowl, combine reserved pear liquid, wine, soy sauce, cornstarch and thyme; mix until cornstarch is dissolved. Gradually add to skillet; cook and stir until mixture thickens. Return chicken to pan; cover and cook 10 minutes. Add pear slices to skillet. Place spinach on top of pears and chicken in skillet; cover and cook 5 minutes or until spinach is wilted and chicken is cooked through.