01 - Preheat the oven to 350°F.
02 - Trim the root and stem ends of the onions. Bring a large pot of salted water to a boil, add whole onions, and simmer for 12–15 minutes until just tender. Drain and let cool slightly.
03 - Carefully peel off the outer layers of each onion, aiming for 2–3 large layers per onion to use for stuffing. Reserve the inner cores for another use or finely chop and add to the filling.
04 - In a bowl, combine ground beef, rice, grated tomato, grated carrot, olive oil, parsley, mint, oregano, garlic, cinnamon, and reserved chopped onion. Season with salt and pepper. Mix until well combined.
05 - Lay out onion layers, place a generous spoonful of filling in the center of each, and roll or fold to enclose the filling securely.
06 - Arrange stuffed onions seam-side down in a baking dish.
07 - In a jug, mix tomato passata, water, olive oil, sugar, salt, and pepper. Pour the sauce over the stuffed onions.
08 - Cover the dish tightly with foil and bake for 50 minutes.
09 - Remove foil and bake for another 20–25 minutes, until golden and the sauce has thickened.
10 - Rest for 10 minutes before serving. Garnish with extra parsley if desired.