Combine the breadcrumbs in a shallow bowl, mixing well. Pre-heat the vegetable oil to 180°C in a large, heavy-based saucepan.
Season the cod, then dust in the plain flour, shaking off any excess. Dip in the beaten egg, then roll in the breadcrumbs making sure each piece is covered evenly. Deep-fry in batches for 3-4 minutes until the breadcrumbs are golden brown in colour.
Meanwhile, whisk together the mayonnaise, yogurt, lemon juice and seasoning until smooth. Fold through the remaining ingredients for the tartare sauce and set to one side. Remove the fish with a slotted spoon and drain on kitchen paper. Remove the fish when ready and spoon generous tablespoons of the tartare sauce on the bottom half of the burger buns. Top with a piece of the fried fish and sprinkle over a little of the chopped parsley.
Place the top halves of the buns on top of the fish. Secure the burgers in place with the wooden skewers. Serve on plates with chunks of lemon on the side.