Preheat oven to 425°F (220°C).

Trim the ends from the zucchini and cut each zucchini crosswise in half. Slice each half lengthwise into ¼-inch (6 mm) thick planks using a sharp knife or mandoline.

Line a baking tray with parchment paper. Arrange the zucchini in a single layer. Lightly brush or spray both sides with olive oil and season with salt and pepper.

Roast for 10–12 minutes, until just tender and beginning to lose moisture. Do not brown.

While the zucchini roasts, heat 1 tablespoon olive oil in a large skillet over medium-high heat.

Cook onion for 4–5 minutes until softened. Add garlic and cook for 30 seconds.

Add ground beef and cook until browned, breaking it up as it cooks. Drain excess fat if necessary.

Add passata, Italian seasoning, paprika, salt, black pepper, and red pepper flakes, if using.

Simmer uncovered for 15–20 minutes, stirring occasionally, until the sauce is thick and very little liquid remains.

Reduce oven temperature to 400°F (200°C).

Lightly grease a 21 × 21 × 6 cm baking dish.

Spread a thin layer of meat sauce over the bottom.

Half the roasted zucchini, half the remaining meat sauce. 1 cup mozzarella

Remaining zucchini, meat sauce, and mozzarella

Top with parmesan, pepperoni, bell pepper, olives (if using)

Bake uncovered for 20–25 minutes, until the cheese is melted and bubbling.

Broil for 2–3 minutes, watching carefully, until golden.

Let the casserole rest for 10–15 minutes before slicing. Garnish with fresh basil, if desired.