Pat the salmon dry, peel and devein the shrimp, and toss both with Cajun seasoning, smoked paprika, salt, and pepper. Let them sit while you heat the pan.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the salmon, skin-side down if using skin. Cook for 3–4 minutes until the edges start to look opaque and a brown crust forms, then flip and cook another 2–3 minutes depending on thickness. Transfer salmon to a plate and tent loosely with foil.

Lower the heat to medium and add the remaining tablespoon of oil and butter. Add the onion and red pepper, sautéing until softened and slightly caramelized, about 4 minutes. Add garlic and cook for 30 seconds until fragrant.

Slide the shrimp into the pan in a single layer and cook for 1-2 minutes per side until they are pink and opaque with a slight curl. If using white wine or broth, splash it in now to deglaze the pan, scraping up browned bits.

Squeeze in lemon juice and stir in chopped herbs. Return the salmon to the skillet to reheat for a minute, spooning some pan sauce over the fillets. Taste and adjust seasoning.