Preheat oven to 375 degrees.
Wash, peel and dice the carrots, golden beets, parsnips, rutabagas and sweet potatoes and add them to a very large bowl. Wash the radishes, slice a small piece off the top and bottoms, then quarter them and add them to the bowl. It is not necessary to peel them.
Add 2 tablespoons of the olive oil, 1/3 cup of the white wine and all the seasonings, salt though pepper. Toss very well to coat.
Evenly spread the root vegetables over two large sheet pans, being sure to pour the marinade evenly over both pans. Roast in the oven for 60-70 minutes, rotating pans and stirring the vegetables occasionally. If the vegetables are looking too dry, you can drizzle with a little more wine and oil.
Meanwhile, heat a large soup pot over medium heat. Add the remaining 2 tablespoons of oil to the pot. Clean and dice the onions and fennel bulb and add to the pot. Sauté, stirring occasionally, for about 30 minutes. It may be necessary to turn your heat to medium low to ensure slow caramelization of the onions and fennel.
Add the minced garlic and turn up the heat to medium high. Cook until fragrant, then add the remaining 1/3 cup white wine and simmer for a couple of minutes.
Add the vegetable stock. Turn the heat to high to bring it to a boil. Stir in the couscous and turn the soup down to simmer. Add the roasted root vegetables and allow to simmer gently on the stove for 15-20 minutes. The couscous will plump up quite a bit.
Season with additional salt and pepper to taste. Serve each bowl of stew topped with a squeeze of fresh lemon juice, toasted walnuts and chopped fresh parsley.