Heat the oven to 200° F and heat the oil to 375° F using either a deep fryer or heavy pot like a Dutch Oven. Line a sheet pan with aluminum foil.
Cut the fish in 3 inch pieces. Place them in a mixing bowl and add the cajun seasoning and lemon juice. Set aside.
In a separate bowl, mix the dry ingredients for the batter - flour, cornstarch, baking soda, cajun seasoning, and salt. Once the oil has reached 375°, mix in the beer. Slowly and gently pour the beer into the mix and fold in using a whisk.
Add some fish to the batter to coat them. When you take them out, let them drip for a second or 2 then add them to the oil. Cook for about 3-4 minutes and transfer them to a plate lined with paper towel to drain the excess oil. Season with a little salt. Then place them on a baking sheet and put it the oven to keep warm until all the fish is cooked.
Once the fish is cooked, cook the fries in the same oil. Cook for about 3-4 minutes. Place the cooked fries on a plate lined with paper towels and season with salt.
Serve the fish and chips with remoulade sauce and ketchup or your favorite sauce.