Optional (for serving)
Position a rack in the middle of the oven and preheat it to 200 °C / 390 °F. Arrange the hazelnuts over a baking sheet and place them into the oven to roast for 8 - 10 minutes. Wrap warm hazelnuts in a kitchen towel and rub nuts in the towel to remove loose skins. Roughly chop it.
make the sauce
Clean the vegetables and peel them if needed. Grate the zucchini, broccoli, and carrots into a small bowl. Place a saucepan with butter, flour, and garlic powder over low heat. Using a whisk, combine and cook for 5 minutes, or until the butter melts and the flour becomes beige. While continuously whisking, pour milk into the mixture to get a smooth sauce. Add the grated vegetables and cook for 10 minutes.
cook the pasta
Place a pot with salted boiling water over medium-high heat. Add your favorite pasta and cook according to the package instructions. Reserve 1/4 cup (60ml) of pasta cooking water before draining the pasta.
finish the sauce
Remove the veggies mixture from the stove and blend slightly using an immersion blender. Add both of the grated cheeses. Stir well with a whisk for the cheese to melt and to get a smooth sauce. Season with salt and pepper to taste. Pour the cheese mixture over the drained pasta and stir well. If needed, add some reserved pasta water to create a more luscious pasta.
Divide the Veggie Mac and Cheese between four pasta plates or bowls. Optionally serve with chopped roasted hazelnuts.