Heat oven to 375 degree F.
Coat a baking sheet with canola oil spray and set aside. Dip fish into egg white and then cornflake crumbs, coating completely. Lay fish fillets on prepared baking tray.
Bake fish fillets for 6 minutes, turn over, and bake an additional 6 minutes, until golden brown.
While fish is baking make tartar sauce by combining yogurt, mayonnaise, and pickle relish; set aside.
Place a fish fillet on the bottom half of each bun. Top with tomato, lettuce, and pickle slices; drizzle with tartar sauce.