Bring a few inches of water to a boil in a large pot with a steamer basket set over it. Place the potatoes and cauliflower in the basket, cover, and steam 15 minutes until very tender.
While the vegetables are steaming, make the gravy. Head olive oil in a small pot on medium-high heat. Add mushrooms, red onion and garlic and sauté 5 minutes until mushrooms are tender and have released liquid. Add flour, stir to combine and cook 1 minute. Add wine and deglaze the bottom of the pot. Once mostly evaporated, add vegetable broth and herbs. Bring to a boil, reduce heat and simmer 5 minutes until slightly thickened. Season with salt and pepper to taste. Cover and set heat to low until ready to use.
Next, make the greens. Heat olive oil in a large skillet on medium high heat. Add kale and cook until wilted, adding a few tablespoons of water every so often to help steam. When mostly wilted, add garlic and white beans and cook another 2-3 minutes.
Place potatoes, cauliflower in a food processor with cashews, almond milk, nutritional yeast, salt and pepper in a food processor. Blend until creamy, adding more almond milk if needed. Mix in scallions if using.
Serve cauliflower mash topped with greens, beans and mushroom gravy.