Pat salmon fillets and shrimp dry with paper towels. Season both sides with 1 tablespoon of the Cajun seasoning.
Heat olive oil in a large skillet over medium-high heat. Place salmon in the pan and sear for 5 minutes per side or until cooked to desired doneness. Remove salmon from the skillet and set aside.
In the same skillet, add the shrimp and sear for 2 minutes per side until pink and opaque. Remove shrimp and set aside.
Reduce heat to medium. Melt the butter in the skillet. Add shallot and garlic, sautéing for 1-2 minutes until fragrant.
Whisk in the heavy cream, chicken broth, and the remaining 1 tablespoon of Cajun seasoning. Bring to a gentle simmer.
Stir in the parmesan cheese until melted and the sauce begins to thicken slightly.
Add the baby spinach to the sauce and stir until wilted. Stir in the lemon juice.
Return the salmon and shrimp to the skillet, spooning the creamy sauce over the seafood. Heat for 1 minute until warmed through.
Garnish with fresh parsley and serve immediately.