Heat the oil in a large pot and sauté the onion gently until soft. Stir often so it doesn’t brown too fast. Then add garlic and mushrooms, cooking until the mushrooms release moisture and deepen in color. This step builds flavor, so don’t rush it.

Add carrots, potatoes, lentils, and tomato paste. Stir well to coat everything evenly. Sprinkle in thyme and drop in the bay leaf. This layering helps flavors develop early. Season lightly, since the stock will add salt later.

Pour in the vegetable stock and bring everything to a gentle boil. Reduce heat and simmer until lentils and potatoes are tender. Stir occasionally to prevent sticking. Taste and adjust seasoning before serving. Remove the bay leaf.