Warm the oil in a large pan over medium heat. Add the mushrooms, baby carrots, and baby onions, cooking for 5–10 minutes. Stir in the minced garlic during the last couple of minutes. The mushrooms should be tender and have released their juices, while the onions and carrots will remain firm.
Increase the heat and pour in the red wine, allowing it to simmer for a few minutes before adding the vegetable stock, tomato purée, fresh thyme, bay leaves, and black pepper. Stir well to combine all ingredients.
If your pan is not oven-safe, transfer the mixture to a casserole dish. Cover with a lid or foil and bake at 190°C (Gas Mark 5 / 375°F) for about 40 minutes, or until the onions and carrots reach your preferred tenderness. Adjust seasoning as needed and serve hot.