Cut each Brussels sprout in half through the root, then slice thinly.
Heat 1 teaspoon of olive oil in a large skillet set over medium heat. Add the onions and cook, stirring occasionally, until the onions are soft, 4 to 5 minutes.
Add the remaining 1 teaspoon of olive oil to the skillet, then add the Brussels sprouts. Cook, stirring occasionally, until the Brussels sprouts are tender, but still bright green.
Stir in the pistachios, dried cranberries, Parmesan cheese and pepper. Taste and season with additional salt, if desired.
Transfer to a serving dish and keep warm until ready to serve.