Preheat the oven to 425°F.
In a large mixing bowl, toss the broccoli florets and Brussels sprout halves with oil, salt, and the black pepper. Arrange the vegetables evenly on a sheet pan, and bake until the vegetables are golden brown, about 18-22 minutes, tossing occasionally. Meanwhile, prepare the pasta.
In a large pot, bring salted water to a boil, and cook the pasta according to the package instructions, then drain well.
In a skillet or saucepan, melt the butter over medium heat. Add the garlic and the crushed red pepper flakes, and continue to cook, stirring constantly, until the garlic softens.
Remove the butter mixture from heat. Stir in the pasta, Parmesan and lemon zest. Add the roasted vegetables, and stir everything until well combined.
Serve immediately. Garnish with extra red pepper flakes and/or extra Parmesan, if desired.