Preheat your oven to 375°F (190°C) and lightly grease a 9x13 inch baking dish.

Slice the zucchinis thinly and place them in a colander; sprinkle with salt and let them sit for 10 minutes to draw out excess moisture.

While the zucchinis are draining, finely chop the onion and mince the garlic.

In a small bowl, mix the sour cream, mayonnaise, dried dill, and paprika to prepare the sauce.

Pat the zucchini slices dry with paper towels to remove any remaining moisture.

In a skillet, heat olive oil over medium heat and sauté the onion and garlic until translucent and fragrant, about 5 minutes.

In a large bowl, combine the sautéed onion and garlic, zucchini slices, salt, pepper, and half of the shredded cheddar cheese. Mix well.

Spread half of the zucchini mixture evenly in the prepared baking dish, then pour half of the sauce over it. Repeat with the remaining zucchini mixture and sauce.

Sprinkle the top with the remaining cheddar cheese, Parmesan cheese, and breadcrumbs.

Bake the casserole in the preheated oven for 35-40 minutes, or until the top is golden brown and the zucchini is tender.

Remove from the oven and let it cool for 5 minutes before garnishing with chopped fresh parsley.

Serve warm as a side dish or a light main course.