In a mixing bowl, toss the halved Brussels sprouts with 2 tablespoons of olive oil, minced garlic, salt, black pepper, and red pepper flakes if using. Spread them out on a lined baking sheet in a single layer.
Roast in the preheated oven for about 20-25 minutes or until the Brussels sprouts are browned and crispy on the edges, stirring halfway through for even cooking.
Meanwhile, bring a large pot of salted water to a boil and cook your pasta according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta.
In a large skillet, combine the cooked pasta, roasted Brussels sprouts, remaining olive oil, lemon juice, and half of the Parmesan cheese. Toss well to combine. If the mixture seems dry, add splashes of the reserved pasta water until desired consistency is reached.
Taste and adjust seasoning with more salt, pepper, or lemon juice as needed.
Serve immediately, topped with the remaining Parmesan cheese and a sprinkle of fresh parsley for garnish.
Notes
Feel free to adjust the amount of red pepper flakes for desired spice level.