1. Preheat oven to 375F.
2. Toast the hazelnuts by placing them on a rimmed baking sheet. Bake for 10 minutes.
3. Remove hazelnuts from the oven and immediately pour into a clean tea towel. Fold the tea towel over the hazelnuts and let them sit for 1-2 minutes.
4. Use the tea towel to rub the hazelnuts to start removing the skins. Pick out the hazelnuts that have the skins removed.
5. Continue until you’ve removed all the skins from the hazelnuts (some of the skins will be stubborn, so don’t worry if it’s not perfect).
6. Let cool while you prepare the rest of the ingredients.
7. While the hazelnuts are in the oven, slice Brussels sprouts very thinly using a mandoline slicer or food processor with a slicer attachment, discarding the stem, to make shaved Brussels.
8. Crush and chop the clove of garlic. Zest lemon until you get 1 teaspoon of zest (per 5 servings). Juice lemon. Core and thinly slice the apple.
9. Chiffonade or mince the mint leaves. To chiffonade mint, stack several leaves on top of each other and slice very thin strips across the leaf all the way down.
10. Dice pancetta.
11. Place pancetta into a cold skillet and turn on heat to medium.
12. Sauté, stirring occasionally, until browned, about 8 minutes. Remove pancetta from the pan and set aside to cool.
13. Combine all of the ingredients into a bowl and toss to combine!
14. If you aren’t going to eat all of it immediately, use the hazelnuts as a garnish instead of mixing them in, since they’ll go a bit soft during storage in the fridge.
15. If you want to make ahead, combine everything except the hazelnuts and then add those at the last minute before serving. Store leftovers in the fridge for up to 5 days.