Preheat oven to 400 degrees Fahrenheit. Line a rimmed baking sheet with parchment paper and set to the side.
Peel and dice the carrots and potatoes. Add them to the baking sheet. In a small bowl, whisk together the grated ginger, garlic, harissa, olive oil, maple syrup, vinegar, and kosher salt.
Pour the mixture over the vegetables and using your hands or a spoon, toss the vegetables to coat in the mixture. Sprinkle with herbs and roast for about 40 minutes until the vegetables begin caramelize slightly and the edges are crisp.
Remove from oven and allow to cool slightly. Keep oven on to toast focaccia croutons. Dice focaccia into ½ inch cubes then place the cubed on a rimmed baking sheet lined with parchment paper. Toast the cubes in the oven for about 7 to 10 minutes until the outer edges are golden and crisp. Remove from oven and set aside.
Using a blender or food processor, blend the roasted vegetables with 1 to 2 cups of the stock. Pour the puréed mixture into a 4-quart dutch oven and add the remaining 4 cups of stock. Stir together well to combine. Allow soup to simmer 10 minutes to thicken slightly.
While the soup warms, prepare the mushrooms. Dice mushrooms into ½ inch pieces.
Preheat a large non-stick or cast iron skillet over medium-high heat with 4 tablespoons olive oil. Add the mushrooms and begin to sauté for 3 minutes until they begin to soften and lightly brown. Add the garlic and fresh herbs then stir to combine. Cook the mushrooms for another 5 to 7 minutes until edges just become crispy.
To serve, ladle the soup into bowls. Top with croutons and crispy mushrooms. Garnish with more chopped fresh herbs, as desired. Serve immediately.