Peel and slice one onion into rings and one potato into thin rounds, then warm them in a frying pan with olive oil, salt, pepper and spices until they begin to soften.
Transfer the onion and potato to a baking dish, arranging them evenly to form a base layer.
Dice two chicken breasts into small cubes, season with salt, pepper and spices, and spread them over the potato and onion layer.
In a bowl, whisk two eggs with Greek yogurt, salt, pepper, dried thyme, turmeric and paprika until smooth and well combined.
Pour the yogurt and egg sauce over the chicken, potato and onion in the baking dish, making sure it covers the chicken and reaches the edges.
Cover the dish tightly with foil and bake at 200∘C for about 40 minutes so the chicken cooks through and the sauce sets gently.
Remove the foil, sprinkle 120 g of grated hard cheese or mozzarella over the hot surface, then arrange tomato slices on top and add a little more cheese over the tomatoes.
Return the dish to the oven uncovered and bake for a further 10 minutes until the cheese has melted and the tomatoes have softened.
Take the dish out of the oven, let it stand briefly, then sprinkle finely chopped fresh herbs over the top.
Serve the bake hot, cutting into portions that reveal the layers of potato, onion, chicken, creamy sauce, cheese and tomato.