1In 12-inch skillet, heat 4 teaspoons of the oil over medium-high heat. Season chicken with salt and pepper; add to skillet. Cook about 10 minutes, turning once, until browned. Remove from skillet; keep warm. In skillet, heat remaining 2 teaspoons oil over medium heat. Add onions and 1/4 teaspoon salt. Cook 10 minutes. Add garlic; cook 15 seconds. Stir in broth. Cook until reduced by half.
2Spray 6-quart slow cooker with cooking spray. Pour onion mixture into slow cooker. Stir in thyme, bay leaves and carrots. Top with chicken. Cover; cook on Low heat setting 6 to 8 hours. Stir in mushrooms. Cover; cook 20 to 30 minutes longer. Remove chicken and vegetables from slow cooker. Discard bay leaves. Increase heat setting to High. Mix cornstarch and water; add to slow cooker, stirring with whisk. Cook and stir 2 minutes, until thickened. Stir in parsley and lemon juice. Serve chicken, vegetables and sauce over mashed potatoes, if desired.