Spray 4- to 5-quart slow cooker with cooking spray. In 10-inch skillet, melt butter over medium-low heat. Cook onions and sugar in butter 30 to 35 minutes, stirring frequently, until onions are deep golden brown and caramelized. Stir in thyme and stew meat; place in slow cooker.
In medium bowl, mix broth and gravy mix; pour over meat mixture in slow cooker. Top with carrots and parsnips. Cover; cook on Low heat setting 8 to 9 hours or until beef and vegetables are tender.
Stir in peas. Cover; cook 10 to 15 minutes longer or until hot.