In a large pot, heat the vegetable oil over medium-high heat. Add the beef stew meat and brown on all sides, about 5-7 minutes.

Add the chopped onion and minced garlic to the pot, and sauté until the onion is translucent, about 3-4 minutes.

Stir in the diced carrots and celery, cooking for another 3-4 minutes until they begin to soften.

Add the rinsed barley, beef broth, diced tomatoes, thyme, rosemary, bay leaf, salt, and pepper. Bring the mixture to a boil.

Reduce the heat to low, cover, and let it simmer for about 1 hour, or until the beef is tender and the barley is cooked.

If using, stir in the chopped spinach during the last 5 minutes of cooking.

Remove the bay leaf before serving. Adjust seasoning with additional salt and pepper if needed.