Cook the pasta in a large pot of salted boiling water according to package instructions until al dente. Reserve about 1 cup of pasta water, then drain and set aside. In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté for 2–3 minutes until translucent. Add the garlic and cook for another 30 seconds until fragrant. Add the salmon cubes to the skillet and cook for 2–3 minutes until lightly browned. Be careful not to overcook the salmon to keep it tender. Deglaze with lemon juice.
Pour in the cream and vegetable broth (or white wine), stirring well. Let the sauce simmer over medium heat for 3–4 minutes until slightly thickened. Season with salt, pepper, and lemon zest. Add the cooked pasta directly to the sauce, tossing to coat evenly. If the sauce is too thick, add some reserved pasta water to reach the desired consistency.
Garnish with fresh dill or parsley and, if desired, sprinkle with Parmesan. Serve immediately.