Bring a large pot of salted water to a boil. Add fettuccine or linguine and cook for 8-10 minutes until al dente. Reserve 1 cup of pasta water before draining.

Season salmon fillet with salt, pepper, and 1 tablespoon of lemon juice. Heat olive oil in a skillet over medium-high heat. Add salmon and cook for 4-5 minutes on each side. Remove from heat and flake.

In the same skillet, sauté garlic for about 30 seconds. Add spinach, cooking until wilted. Pour in heavy cream and stir to combine.

Gradually incorporate Parmesan cheese into the skillet, stirring until melted. Add lemon zest, lemon juice, and red pepper flakes; let simmer for 2-3 minutes.

Add the drained pasta to the skillet, tossing to combine. Fold in flaked salmon, adjusting the sauce with reserved pasta water if needed.

Plate the pasta dish and garnish with chopped parsley. Serve immediately.