Make the pasta – Boil a pot of salted water and cook the pasta according to package instructions until al dente. Save about ½ cup of pasta water before draining.
Sear the salmon - Pat the salmon fillets dry with a paper towel, then season both sides with onion powder, salt, and black pepper. In a large skillet, heat the olive oil over medium-high heat. Add the salmon, skin side down (if skin-on), and sear for about 3-4 minutes until golden and crispy. Carefully flip and cook for another 2-3 minutes, until the salmon is cooked through (145°F) and flakes easily with a fork. Transfer to a plate and set aside.
Creamy Garlic Sauce – In the same skillet, reduce heat to medium and melt the butter. Sprinkle in the flour and cook for about 30 seconds, stirring. Stir in the garlic powder (or minced fresh garlic) and sauté until fragrant, about 30 seconds. Add the broth and simmer for 1–2 minutes to deglaze the pan, scraping up bits of salmon.
Stir in the cream and cheese — Add the heavy cream and warm it through. Add the grated Parmesan cheese in batches to the sauce, stirring constantly until completely melted and the sauce is smooth and creamy. Add salt, black pepper and, if using, red pepper flakes to taste.
Combine everything — Use a fork to flake the cooked salmon into bite-size bits and add it back to the skillet. Stir in the drained pasta and toss everything together so the pasta is well coated in the sauce. If it needs it, add a splash or two of reserved pasta water, to loosen the sauce.
Finishing touches — For brightness, stir in a squeeze of fresh lemon juice, and then sprinkle the plate with chopped parsley or dill. Serve immediately and enjoy!