Cut the tops off each mini pumpkin and scoop out the seeds and strings. Set the hollowed pumpkins aside.
Heat the olive oil in a large pot over medium heat. Add the beef cubes and brown them on all sides.
Stir in the onion, carrots, celery, and garlic. Cook for a few minutes until the vegetables soften.
Pour in the beef broth and diced tomatoes. Add the barley, thyme, and a pinch of salt and pepper.
Bring the mixture to a simmer, then cover the pot and cook for about 45 minutes until the beef is tender and the barley is cooked through.
While the stew simmers, place the hollowed pumpkins on a baking sheet and warm them in a 350 degree oven for 10 minutes.
Ladle the finished stew into the warmed pumpkins and serve right away.