Heat a heavy skillet over high heat for 15 to 20 minutes. Mix mayonnaise with 1 to 2 teaspoons of Cajun spice. Taste, add salt, pepper or more Cajun spice as necessary; put aside till later.
Lightly oil both sides of the salmon and sprinkle with the remaining Cajun spice (the more you add, the hotter it becomes, so heads up).
Place salmon in the hot skillet to blacken; cook 2 to 3 minutes on the first side, turn and finish cooking. Cooking time will vary based on the thickness of fish and the heat of pan. Spread 1 tablespoon of the mayonnaise mixture onto each French roll. Top each with a
blackened salmon steak/fillet, 2 slices of tomato and 1/4 cup of the shredded cabbage and serve.