Prepare the Chicken:

In a bowl, beat eggs with mayonnaise and parsley. Gradually whisk in flour to form a smooth batter.
Season chicken filets with salt, black pepper, and oregano. Let marinate for 10 minutes.
Prepare the Potatoes:

In a bowl, toss diced potatoes with salt, black pepper, rosemary, garlic powder, sweet paprika, and olive oil. Let sit for 7-10 minutes to absorb flavors.
Prepare the Vegetables:

Sprinkle zucchini slices with salt and let sit for 7-10 minutes to release moisture. Pat dry with a paper towel. Toss with olive oil.
Heat olive oil in a skillet and sauté onion until soft. Add minced garlic and sliced mushrooms, cooking until tender. Season with salt.
Assemble the Bake:

Preheat the oven to 190°C (375°F).
In a greased baking dish, layer potatoes, zucchini, and the sautéed onion-mushroom mixture.
Dip marinated chicken filets into the batter, ensuring they are well coated, and place on top of the vegetables.