In a large pot, heat 1 tbsp of the olive oil over medium heat. Add the onions, mushrooms and garlic. Continue to cook over medium heat until the vegetables are softened (about 10 minutes). Add a splash of water if the mixture dries out.
Add the remaining ingredients and bring to a boil. Reduce to a simmer, cover and cook on low for 1 hour.
Serve with polenta, brown rice or quinoa, and freshly chopped parsley.