In a large skillet, heat the olive oil over medium-high heat. Add the beef cubes in batches and brown on all sides. Transfer the browned beef to the slow cooker.
In the slow cooker, add the onion soup mix, beef broth, carrots, potatoes, celery, garlic powder, thyme, bay leaf, salt, and pepper. Stir to combine.
Cover and cook on low for 7-8 hours or on high for 4-5 hours, until the beef is tender and the vegetables are cooked through.
Remove the bay leaf before serving. Taste and adjust seasoning if necessary.
Serve hot with crusty bread or over rice, if desired.