Heat a pan over medium heat. Once heated, add the onions and leeks; cook for 5 to 6 minutes, until the onions are soft and transparent. Add the garlic and mushrooms, then cook for an additional 2 to 3 minutes. Add the carrots and sauté for 1 to 2 minutes, then cover with vinegar and water. Add the potatoes, lentils, cauliflower, oats, thyme, and bay leaf.