Place the cubed beef stew meat in the bottom of the slow cooker.
Add the sliced leeks, carrots, and potatoes on top of the beef.
Pour in the beef broth, then stir in the lemon zest, thyme, rosemary, salt, and black pepper.
Cover and cook on low for 7 to 8 hours until the beef is tender and the vegetables are soft.
Stir in the frozen peas during the last 30 minutes of cooking so they stay bright and tender.
Turn off the heat and stir in the lemon juice and chopped parsley just before serving.