Preheat oven to 220 °C or 210 °C fan bake. Line an oven tray with baking paper.
Cook chips
Wash and slice the unpeeled 600 g potatoes and 200 g sweet potato into chunky chips. Toss them on the prepared oven tray with 1 tbsp olive oil and season with salt and pepper. Bake in the oven for 22-25 minutes or until tender and crispy.Note: If using frozen chips cook according to packet directions.
Prep chicken
Pat 600 g chicken breast dry. Place your hand flat on top of the chicken and slice through horizontally. Add ¼ cup cornflour to a plate. Whisk 1 egg in a separate shallow bowl and add ½ cup Southern style seasoning to a separate plate. Coat the chicken in the cornflour, then dip into the egg to coat and then press firmly into the Southern style seasoning to coat.
Cook chicken
Heat 1 tbsp olive oil in a large frypan over medium-high heat. Add the crumbed chicken (cook in batches if needed), and cook for 3-4 minutes on each side, or until golden and cooked through. Transfer to a paper towel-lined plate.
To finish
Meanwhile, thinly slice ½ iceberg lettuce. Cut 50 g cheese into slices. Cut 4 burger buns in half. When the chips have 5 minutes of cooking time remaining, add the burger buns cut side up on the top rack in the oven and cook for 5 minutes, or until golden.
To serve
Top the burger bun bases with the mayonnaise, lettuce, crispy chicken, cheese and bun top. Divide the burgers and chips between plates with tomato sauce on the side for dipping.