Preparation

• Bring a large pot of well-salted water to a boil. Meanwhile, heat the oil in a 12-inch skillet over medium heat. Add the pancetta and cook, stirring occasionally, until crisp, about 5 minutes. Using a slotted spoon, transfer the pancetta to a paper-towel-lined plate. Add the garlic to the skillet and cook, swirling the pan, until fragrant, 30 seconds. Remove and discard the garlic. Add the red pepper flakes, Brussels sprouts, and 1/2 tsp. salt. Cook, tossing with tongs, until the sprouts are crisp-tender, 2 to 3 minutes. Stir in half of the Parmigiano and the lemon juice and remove from the heat.
• Boil the pasta according to package directions until al dente. Reserve 1/2 cup of the cooking water, drain the pasta, and then add it to the skillet along with 1/4 cup of the reserved water.
• Cook over medium-high heat, tossing and adding more water as needed, until the Brussels sprouts are tender, about 1 minute. Stir in the pancetta and season generously with black pepper. Taste and season with additional salt and lemon juice, if you like. Serve topped with the hazelnuts and the remaining Parmigiano.