Place mince, onions and Cajun seasoning in a large bowl. Season, mix well and form into 4 patties. Heat a large lightly oiled non-stick frying pan over medium heat. Cook burgers for 3-4 minutes each side or until cooked to your liking. Set aside on a plate loosely covered with foil. Lightly spray eggplant with oil. Reheat same pan over medium-high heat and cook eggplant, in batches, if necessary, for 1-2 minutes each side or until lightly browned. Set aside on a plate lined with paper towel.
In a small bowl combine yogurt and coriander. Season.
Divide patties, tomatoes, pickles and eggplant between 4 lettuce leaves. Top with yoghurt. Serve with remaining lettuce leaves, any remaining yoghurt, coriander sprigs and sweet potato fries.
Instead of mince sprinkle rump or minute steak with seasoning, and serve sliced in lettuce leaves.
Moroccan or lemon pepper seasoning or fresh/dried herbs would also be great in the beef patties.
Swap yoghurt for whole egg mayonnaise, if desired.