01 - Preheat the oven to 375°F. Grease a 9x13-inch casserole dish with cooking spray or butter.
02 - Heat 1 tablespoon olive oil in a large skillet over medium heat. Add ground beef and cook until browned, about 5–6 minutes. Drain excess fat.
03 - Add onion and garlic to the skillet. Sauté for 2–3 minutes until softened and fragrant.
04 - Stir in drained diced tomatoes, oregano, basil, paprika, salt, and pepper. Cook for 3–4 minutes to blend flavors, then remove from heat.
05 - In a separate bowl, whisk together sour cream, milk, and half of the cheddar cheese until smooth.
06 - Arrange half of the zucchini slices in a single layer at the bottom of the prepared casserole dish.
07 - Spread half of the seasoned beef mixture evenly over the zucchini layer.
08 - Dollop half of the sour cream mixture over the beef and gently spread to cover.
09 - Layer remaining zucchini slices, followed by remaining beef mixture, then remaining sour cream mixture.
10 - Sprinkle remaining cheddar cheese, Parmesan, and breadcrumbs over the top. Drizzle with remaining 1 tablespoon olive oil.
11 - Cover tightly with aluminum foil and bake for 25 minutes until zucchini is tender.
12 - Remove foil and bake an additional 15 minutes until cheese is melted and golden brown with bubbly edges.
13 - Let casserole stand for 5–10 minutes before serving to allow layers to set for easier slicing.