Remove stalks from mushrooms and chop them. Heat oil in a large saucepan and cook onion over medium heat for 2-3 minutes, or until soft. Add garlic and mushroom stalks and cook for a further minute. Stir in lentils, wine and stock; bring to boil. Reduce heat and simmer, covered, for 20-25 minutes, stirring occasionally, or until reduced and lentils are cooked through. If mixture is too wet, remove lid and boil until slightly thick. Stir in parsley and keep warm.
Meanwhile, make bean puree. Bring small saucepan of water to boil over high heat and cook potato for 10 minutes, or until tender. Drain and mash with a potato masher until smooth. Stir in half extra virgin oil. Combine cannellini beans and garlic in a food processor. Add stock and remaining oil and process until smooth. Transfer to a bowl and fold in mashed potato. Keep warm.
Melt butter in a deep frying pan. Add mushrooms and extra garlic; cook in batches over medium heat for 4 minutes each side, or until tender. Remove and keep warm.
To make red wine sauce, add red wine to the same frying pan, then scrape the bottom to remove any sediment. Add combined tomato paste, stock and sugar; bring to boil. Cook for about 10 minutes, or until reduced and thickened.
To assemble, place mushrooms onto serving plates; top with the bean puree. Spoon on the lentil mixture & drizzle with the red wine sauce. Season and serve immediately.