Cut eggplants into 1cm slices; sprinkle with 1 teaspoon salt and let stand for 20 minutes; soak up the liquid with a paper towel.
Preheat an oven to 180 degrees C.
Heat the olive oil in a frypan over medium heat; brown the onion and cook meat in the hot oil. Stir in the walnuts and cook another 2 minutes; remove from heat.
Arrange half of the eggplant slices in the bottom of a 20 x 30cm baking dish; spoon the beef mixture over the layer of eggplant. Top the beef mixture with the remaining eggplant slices, potatoes and tomatoes; season with salt and pepper.
Bake uncovered in preheated oven until the eggplant is soft; about 1 hour.