Heat oil in a large pot over medium-high heat. Sauté onion, garlic, and bay leaf in hot oil until onions are translucent, about 5 minutes. Add water, peas, barley, and salt; bring to a boil. Reduce heat to low and simmer for 2 hours, stirring occasionally.
Add potatoes, carrots, celery, parsley, basil, thyme, and pepper. Simmer until peas and vegetables are tender, about 1 hour.