Bring a medium pot of salted water to a boil and cook the pasta according to package instructions. Drain and set aside.
Heat olive oil in a large skillet over medium heat and sauté the onion until tender. Add the milk and cream cheese and stir until the cream cheese melts and the sauce becomes smooth.
Stir in capers and lemon juice. Add the smoked salmon, then toss in the spinach and cook until just wilted.
Add the pasta and toss until everything is well combined.
Serve immediately and add fresh dill and grated cheese on top.