Bring a pot of water to a boil over high heat. Season generously with salt and cook the pasta 3 minutes less than the packet instructions. Remove and drain.

In a large saucepan over medium-high heat, add the butter and let it melt. Add the onion and garlic and sauté for 2 minutes, mixing regularly, until the onion starts to soften. Add the flour and mix well. Cook for 2 minutes, until thickened and starting to bubble — don't let it brown. Slowly add the warmed milk in batches, mixing between each addition until fully absorbed. Once combined, add the cream and cook for 1 minute. Check the seasoning and remove from the heat.

Add the drained pasta, flaked tuna, and lemon zest to the sauce and mix really well until combined. Transfer to the greased baking dish and spread evenly. Sprinkle over the panko breadcrumbs and cheese, distributing both evenly, and bake for 30–35 minutes, or until golden on top. Remove and rest for 10 minutes before serving.

Serve on plates or in bowls, garnished with cracked black pepper and flat leaf parsley, if using. Dig in.