In heatproof bowl, place porcini mushrooms and boiling water. Let mushrooms rehydrate for 15 minutes. Strain, making sure to save both rehydrated mushrooms and mushroom broth.

Finely chop mushrooms and set both mushrooms and broth aside.

In large stock pot or Dutch oven, warm oil over high heat. Add mixed mushrooms (except chopped porcini mushrooms) and allow to sear, stirring only very occasionally, until well browned, about 6 minutes. Turn heat down to medium and stir in onion. Cook, stirring often, for 3 minutes before adding reserved chopped porcini mushrooms, minced garlic, and tomato paste. Continue to cook, stirring often, for 2 minutes. All vegetables should be well covered in tomato paste and some should be sticking to the bottom of the pot.

Deglaze bottom of pot with 1 cup reserved mushroom broth. Stir in diced tomatoes along with their juices, vegetable broth, remaining mushroom broth, lentils, and wild rice. Bring to a simmer before stirring in cabbage, bay leaf, and thyme. Cover pot with lid and cook on low, stirring occasionally, until lentils and rice are tender, about 40 to 45 minutes. Stir in vinegar and salt and let soup continue to cook for another 2 minutes. Remove from heat and stir in about 1/2 cup parsley (if using).

When ready to serve, ladle soup into bowls and garnish with some more parsley if desired. Eat while warm.