Slice the chicken breasts and place into a bowl. Season with the chicken seasoning and mix to combine.
Add all the seasoned flour ingredients, except the egg, to a bowl and mix to combine. In a separate bowl, crack and whisk the eggs.
Dip the chicken into the egg, coating well, then transfer to the seasoned flour and coat thoroughly. Shake off any excess and place onto a lined baking tray or into an air fryer basket. Spray lightly with cooking oil.
If baking, cook at 200°C (390°F) for 22–23 minutes, flipping halfway, until golden and the internal temperature reaches 74°C (165°F). If air frying, cook at 190°C (375°F) for 15–16 minutes, flipping halfway, until cooked through.
In the meantime, mix all the burger sauce ingredients and refrigerate until ready to assemble.
Toast the buns, or leave them fresh. Spread the burger sauce evenly across the top and bottom buns. Add the chicken and top with lettuce just before eating.
Wrap tightly in food-safe paper or foil and serve.