Prepare the Chicken: Preheat your oven to 190°C (170°C fan/Gas Mark 5). Heat the olive oil in a large, oven-safe frying pan or casserole dish over medium-high heat. Add the cubed chicken breast and cook for 3-5 minutes, stirring occasionally, until the chicken cubes are lightly browned on all sides and no longer look raw, though they don't need to be cooked through. You'll notice a lovely golden crust forming. Remove the chicken from the pan and set aside.

Sauté Aromatics: In the same pan, add the diced onion and cook for 3-4 minutes until it softens and becomes translucent, releasing a sweet aroma. Stir in the minced garlic and chilli flakes (if using) and cook for another minute until fragrant, being careful not to let the garlic burn. The kitchen will begin to smell wonderfully savoury.

Build the Sauce: Pour in the passata, chopped tomatoes, and chicken stock. Add the dried oregano, dried basil, and granulated sugar. Season generously with salt and black pepper. Stir everything together well until the sauce is uniform and gently bubbling, taking on a rich, deep red colour.

Combine & Bake: Stir the dried penne pasta directly into the sauce. Add the partially cooked chicken back into the pan, ensuring it's submerged in the sauce. Cover the pan tightly with a lid or aluminium foil. Transfer the pan to the preheated oven and bake for 25 minutes.

Cheesy Topping: After 25 minutes, carefully remove the pan from the oven. The pasta should have absorbed most of the liquid and look slightly al dente, and the sauce will be thicker. Give it a gentle stir. Sprinkle the grated mozzarella and Parmesan cheeses evenly over the top of the pasta.

Final Bake & Rest: Return the uncovered pan to the oven and bake for another 10-15 minutes, or until the cheese is melted, bubbly, and beautifully golden brown on top, with a satisfying sizzle. Let the dish rest for 5-10 minutes out of the oven before serving. This allows the sauce to settle and the pasta to absorb any remaining liquid, resulting in a perfectly tender texture.