Pat and season the salmon: Pat the fillets dry. Season both sides with 1 teaspoon kosher salt, 1/2 teaspoon black pepper, and 1 teaspoon Italian seasoning.
Zest the lemon and reserve the zest for later.
Sear the salmon: Heat 1–2 tablespoons olive oil in a large skillet over medium-high. Place salmon skin-side up and sear 3–4 minutes until golden. Flip and cook 2–4 minutes more, depending on thickness.
Transfer to a plate; tent loosely with foil.
Sauté aromatics: Lower heat to medium. Add a drizzle of oil if needed. Cook onion or shallot 2–3 minutes until softened.
Add garlic and sun-dried tomatoes; cook 30–60 seconds until fragrant.
Build the sauce: Stir in 1/2 cup broth and scrape up browned bits. Reduce heat to medium-low. Add 1/3–1/2 cup half-and-half (or light coconut milk).
Simmer gently 2 minutes to thicken slightly. Avoid a hard boil to prevent curdling.
Add spinach: Stir in spinach by the handful until wilted, 1–2 minutes. If using frozen spinach, make sure it’s well squeezed and warmed through.
Finish the flavor: Stir in lemon zest and 1–2 teaspoons lemon juice.
Add a pinch of red pepper flakes and 2–3 tablespoons grated Parmesan if using. Taste and season with more salt and pepper as needed.
Optional Greek yogurt boost: If using, whisk 1/4 cup Greek yogurt with a few tablespoons of the warm sauce in a small bowl, then stir back into the skillet off heat. This keeps it silky and prevents splitting.
Nestle the salmon back: Return the salmon to the pan, spoon sauce over the top, and warm 1–2 minutes on low.
Sprinkle with chopped basil or parsley.
Serve: Plate salmon with a generous spoonful of spinach-tomato sauce. Add extra lemon on the side. Pair with quinoa, whole-wheat pasta, or roasted vegetables.