In a large bowl, mix the minced meat, grated onion, garlic, egg, breadcrumbs, parsley, baking soda, and spices. Knead until well combined.
Cover and rest the meatball mixture in the fridge for 20–30 minutes.
Shape the mixture into small meatballs, oiling your hands lightly to prevent sticking. Set aside.
Slice the eggplants and soak them in salted water for 15–20 minutes. Drain and pat dry.
Toss the eggplant slices with powdered pepper, salt, and liquid oil.
Arrange the meatballs and eggplant slices alternately on a baking tray.
In a small saucepan, simmer the tomato sauce, oil, and water for a few minutes, then pour evenly over the tray.
Cover with oiled baking paper and bake at 190°C (375°F) for 35–45 minutes, until the eggplant is golden and tender.
Remove the paper for the last few minutes for extra color, then serve warm.