Bring a large pot of salted water to a boil. Cook the penne pasta until al dente. Reserve 1/2 cup of pasta water, then drain the pasta and set aside.

Pat the salmon fillets completely dry and season generously with salt and pepper. Heat olive oil in a large skillet over medium-high heat.

Sear the salmon for 4-5 minutes flesh-side down, flip, and cook for another 3-4 minutes until golden and cooked through. Remove from pan, discard skin, and flake into large chunks.

Reduce heat to medium-low. Add butter to the same skillet. Once melted, add minced garlic and sauté for 1 minute until fragrant.

Whisk in the heavy cream, scraping up the browned bits from the bottom of the pan. Let simmer gently for 2-3 minutes to slightly thicken.

Lower heat to low. Whisk in the freshly grated Parmesan cheese until melted and smooth. Stir in the fresh baby spinach and cook for 1-2 minutes until wilted.

Add the cooked pasta to the skillet, tossing to coat in the cream sauce. If the sauce is too thick, add a splash of the reserved pasta water. Stir in the lemon juice.

Gently fold in the flaked salmon. Garnish with fresh parsley and serve immediately.