Place a large, heavy skillet over high heat for 10 minutes. Mix the mayo with 1 to 2 teaspoons of Cajun seasoning.
Taste, then add salt, pepper or more Cajun seasoning as necessary (BUT BE CAREFUL: THE MORE YOU ADD, THE HOTTER IT BECOMES!). Set aside. Lightly rub the olive oil into both sides of fillets then sprinkle with remaining Cajun seasoning.
Place salmon in the hot skillet to blacken. Cook for 2 to 3 minutes on the first side then turn and finish cooking. Cooking time will vary, depending on the thickness of the fish and the heat of the pan.
Spread 1 tablespoon of the mayonnaise mixture on each French roll then top with a blackened salmon fillet, 2 slices of tomato and a 1/4 cup of the shredded cabbage. Serve and enjoy!