To roast the nuts: Toast the hazelnuts over medium heat in a small dry skillet for 2-3 minutes, or until fragrant. Once cool enough to handle, place the nuts in a clean, dry kitchen towel and rub them vigorously to remove the skins.
Preheat oven to 425°F / 220°C degrees and line a baking sheet with parchment paper.
Transfer the vegetables to the baking sheet and toss with the oil. Season with 1/2 teaspoon salt (or more) and toss again. Spread the vegetables into an even layer (without crowding them) and roast for 20-25 minutes, tossing halfway through, until lightly browned and tender.
Meanwhile, in a food processor (alternatively using a mortar with a pestle), combine the hazelnuts, parsley, garlic, oil, and lemon zest. Process into a rough paste. Set aside.
Transfer the roasted vegetables to a serving platter and drizzle with the lemon juice. Then scatter the hazelnut gremolata on top. Season with more salt if desired. Serve and enjoy!
Parsnips will cook at about the same rate as carrots, so cut them into similar-size pieces. If using a larger parsnip, then you can cut the bottom smaller part in half, and the larger top half into thirds or quarters (lengthwise) so everything is about the same size and cooks evenly.
I always use olive oil for roasting my vegetables. My favorite is extra-olive oil from Farchioni Olii which is also heat resistant, making it great for cooking and for salads. Plus it tastes amazing.
As an alternative to roasting the hazelnuts, already roasted hazelnuts can be found in your local organic food store.