Salmon is assertive in flavor and will hold its own superbly combined with robust ingredients like bitter greens, sharp cheese, garlic, and red-pepper flakes.
Cook pasta in a large pot of generously salted boiling water until al dente; add broccoli rabe 2 minutes before pasta is done. Reserve 1 cup pasta water; drain pasta and broccoli rabe.
Combine oil, garlic, and red-pepper flakes in pot over medium. Cook, stirring, until garlic is just softened, about 2 minutes. Add pasta, broccoli rabe, and cheese to pot; toss to coat. Add reserved pasta water, a little at a time, until sauce evenly coats pasta. Gently fold in salmon. Serve, with more cheese and red-pepper flakes and a drizzle of oil.