Add the beef stew meat, mushrooms, onion, carrots, and garlic to the slow cooker.
In a small bowl, whisk together the beef broth, tomato paste, Worcestershire sauce, thyme, salt, and pepper until smooth.
Pour the broth mixture over the ingredients in the slow cooker and stir to combine.
Cover and cook on low for 7 to 8 hours until the beef is tender.
Stir in the frozen peas and let them warm through for the final 30 minutes of cooking.
Spoon the beef mixture into bowls and top each serving with a generous layer of mashed potatoes.