Add the oil to a large stock pot over medium-high heat, and then add the leek, garlic, and carrots to the pot. Cook until the vegetables are soft and have browned slightly, about 10 minutes.
Add the stock, split peas, potato, thyme, salt, and pepper to the pot. Bring to a boil and then reduce the heat to a simmer.
Cover the pot and allow the soup to simmer for 60 to 90 minutes, or until the peas have softened, the potatoes are tender, and the soup has reached the desired consistency.