Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente.

Reserve 1 cup of pasta water, then drain the pasta in a colander.

In a skillet, heat olive oil over medium heat. Season the salmon fillet with salt and pepper.

Cook the salmon for about 4-5 minutes on each side or until it flakes easily with a fork. Remove from skillet and set aside.

In the same skillet, add diced onion and minced garlic. Sauté until the onion is translucent.

Pour in the chicken broth and bring to a simmer. Stir in the heavy cream, lemon juice, and dill. Cook for 2-3 minutes until slightly thickened.

Add the cooked pasta and spinach to the skillet. Toss to combine and cook until the spinach wilts.

Flake the cooked salmon and gently fold it into the pasta mixture. If the sauce is too thick, add reserved pasta water to reach desired consistency.

Serve immediately, garnished with additional dill if desired.