Season the salmon. Pat fillets dry and season both sides with salt and pepper.
Dry surfaces sear better and help keep the fish juicy.
Sear the salmon. Heat olive oil in a large skillet over medium-high. Place salmon in the pan, presentation side down. Sear 3–4 minutes until golden.
Flip and cook another 2–4 minutes, depending on thickness. Transfer to a plate; tent loosely with foil.
Build the flavor base. Reduce heat to medium. Add butter to the same skillet.
Sauté garlic for 30 seconds until fragrant, stirring so it doesn’t brown.
Add tomatoes and deglaze. Stir in sun-dried tomatoes. Pour in broth and scrape up any browned bits. Those bits are pure flavor and make the sauce taste slow-cooked.
Make it creamy. Pour in heavy cream and Italian seasoning.
Simmer gently for 2–3 minutes, stirring. Avoid a hard boil to prevent the cream from separating.
Melt the cheese. Sprinkle in Parmesan a little at a time, stirring until smooth. Adjust thickness with a splash more cream or broth as needed.
Add spinach and heat through. Fold in spinach until just wilted.
Season with salt, pepper, and red pepper flakes if using. Finish with lemon juice for brightness.
Return the salmon. Nestle fillets into the sauce, spooning sauce over the tops. Simmer 1–2 minutes to rewarm and let flavors meld.
Taste and adjust seasoning.
Serve. Plate with extra sauce over the salmon. Add lemon wedges. For keto sides, think zucchini noodles, roasted asparagus, sautéed green beans, or cauliflower mash.