Using a mandoline or a sharp chef's knife, thinly shave the Brussels sprouts into a large mixing bowl.
In a separate small bowl, whisk together the extra-virgin olive oil, lemon juice, Dijon mustard, honey, salt, and black pepper until the dressing is fully emulsified.
Pour the dressing over the shaved Brussels sprouts and toss thoroughly to ensure even coating.
Add the toasted walnuts, dried cranberries, and grated Pecorino Romano to the bowl.
Toss the ingredients gently to combine.
Allow the salad to rest at room temperature for 10 to 15 minutes before serving to let the flavors meld and the sprouts soften slightly.