To make the tartar sauce, combine mayonnaise, pickle relish, onion, lemon juice, parsley, and cajun seasoning in bowl and stir to blend. Refrigerate until ready to serve.
To make the fries, preheat oven to 425F. Toss potatoes to evenly coat with olive oil, garlic powder, onion powder, cajun seasoning, salt and pepper in a large mixing bowl and spread in a single layer on a baking sheet. Bake for 30 to 40 minutes until golden brown and crispy, turning the potatoes halfway.
Meanwhile, arrange fish on a baking sheet lined with parchment paper and bake for 23 to 25 minutes or until fish is crispy, golden and cooked through.
Serve fish fillets and fries with tartar sauce and lemon wedges.