Heat oil in a large skillet over medium-high heat. Sprinkle salmon with one teaspoon Cajun seasoning, two tablespoons Parmesan cheese, and pepper, then add to the skillet, skin-side up. Cook until deeply golden, about six minutes, then flip and cook two minutes more. Transfer to a plate.

Add butter and garlic to skillet. When butter has melted, stir in broth, lemon juice, honey, remaining teaspoon Cajun seasoning, parsley, and remaining two tablespoons Parmesan cheese. Bring to a simmer.

Reduce heat to medium and return salmon to the skillet. Simmer until sauce has reduced and salmon is cooked through, three to four minutes.

Add lemon slices and serve.