In a large pot or Dutch oven, heat the olive oil over medium-high heat. Add the beef stew meat and brown on all sides, about 5-7 minutes. Remove the beef and set aside.
In the same pot, add the diced onion and garlic. Sauté until the onion is translucent, about 3-4 minutes.
Add the carrots and celery to the pot, cooking for an additional 3-4 minutes until they begin to soften.
Return the browned beef to the pot. Stir in the pearl barley, beef broth, thyme, rosemary, bay leaf, salt, and pepper. Bring to a boil.
Reduce the heat to low, cover, and let simmer for about 1 hour, or until the beef is tender and the barley is cooked.
If using, stir in the frozen peas during the last 5 minutes of cooking.
Remove the bay leaf before serving. Garnish with fresh parsley if desired.