Place chicken and onion in slow cooker. In a bowl, whisk together curry paste, soy sauce, chicken broth, brown sugar, and peanut butter. Pour into slow cooker. Set on low for about 6 hours or until chicken is cooked through. Add coconut milk and vegetables and cook for another hour. Remove chicken and shred, then return to slow cooker.
I adapted this recipe from monicaswanson.com