Prep the salmon: Pat fillets dry. Season both sides with salt and pepper.
If using skin-on salmon, keep the skin on.
Sear the fish: Heat a large skillet over medium-high. Add 1 tablespoon oil and 1 tablespoon butter. Place salmon skin-side down and cook 3–4 minutes until the skin is crisp.
Flip and cook 2–3 minutes more, just until almost cooked through. Transfer to a plate; tent loosely with foil.
Sauté aromatics: Lower heat to medium. In the same skillet, add a touch more oil if needed.
Add minced garlic and a pinch of red pepper flakes. Stir 30 seconds until fragrant.
Build the sauce: Pour in 1/2 cup chicken broth to deglaze, scraping up browned bits. Simmer 1 minute.
Stir in 3/4 cup heavy cream, 1/3 cup grated Parmesan, and the sliced sun-dried tomatoes.
Season and thicken: Add 1 teaspoon Italian seasoning, a pinch of salt, and black pepper. Simmer 2–3 minutes, stirring, until slightly thickened and silky.
Add greens: Fold in a couple handfuls of spinach. Let it wilt, about 1 minute.
Taste and adjust salt, pepper, and heat.
Finish with brightness: Add 1–2 teaspoons fresh lemon juice and a little zest. This balances the creamy sauce.
Return the salmon: Nestle fillets back into the sauce, spooning sauce over the top. Simmer 1–2 minutes to finish cooking.
Salmon should be just opaque and flaky, around 125–130°F in the thickest part for medium.
Garnish and serve: Top with chopped basil or parsley and extra Parmesan. Serve with cauliflower rice, zucchini noodles, steamed asparagus, or a crisp salad.