Heat the olive oil in a large pot over medium heat. Add the ground beef and cook until browned, breaking it up with a spoon as it cooks.
Add the diced onion, carrots, and sliced mushrooms to the pot. Cook for 5 minutes until the vegetables begin to soften.
Stir in the minced garlic and dried thyme, then cook for 1 minute until fragrant.
Add the pearl barley and beef broth. Season with salt and black pepper.
Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 40 minutes, stirring occasionally, until the barley is tender.
Let the stew cool completely before portioning into freezer-safe containers.