Take your fish out of the fridge and bring to room temperature while you prepare the sauce.
Make cilantro cream sauce by adding all the above cream sauce ingredients in a blender on medium speed and blend until smooth. Set aside
Make sure your fish is not ice cold or it will not cook evenly. If it needs more time give it another 10 minutes to come to room temperature. Season both sides of fish with Cajun seasoning. In a nonstick sauté pan over medium high heat warm oil. Carefully place the fish in the pan, away from you and cook uncovered for 2-3 minutes. Using a fish spatula and fork to help flip the fish onto other side. Cook for another 2-3 minutes, or until opaque in the center. Remove from heat.
Spread sauce on bottom of the bun, add fish and squeeze your lemon or lime over the fish. Top with tomato, lettuce and red onion. Serve with pickles, coleslaw, French Fries or potato salad.