Make the green chile sauce: Heat the olive oil in a large saucepan over a medium flame until it shimmers and smells fragrant. Add the diced onion and cook for 5–7 minutes, stirring occasionally, until it turns translucent and softens. You’ll know it’s ready when the onion releases a sweet, savoury aroma and begins to catch the light. Stir in the minced garlic and cook for another minute until it smells pungent and mellow.

Build the sauce base: Add the chopped green chillies, chicken stock, double cream, cumin, and oregano to the pan. Bring the mixture to a gentle simmer—you’ll see small bubbles breaking the surface and the liquid will thicken slightly, turning a pale green shade with flecks of chilli. Season with salt and pepper, then let it bubble away for 10 minutes, stirring now and then. The sauce should coat the back of a spoon.

Prepare the chicken filling: In a large bowl, combine the shredded chicken with about half of the green chile sauce. Stir until every strand of meat is well coated. The chicken will absorb the sauce, turning it a warm, creamy colour and releasing a heady, spicy scent.

Assemble the casserole: Preheat your oven to 180°C (fan-assisted). Spread a thin layer of the remaining sauce across the bottom of a 23x33cm baking dish. Take three tortillas and tear them into rough quarters, then arrange them over the sauce to create a base layer. Spoon half of the sauced chicken mixture over the tortillas, spreading it evenly. Sprinkle with a third of the combined mozzarella and cheddar.

Layer again: Repeat the process—another layer of torn tortillas, the remaining chicken mixture, and another third of the cheese. The dish will start to look wonderfully messy and abundant, with tortilla edges peeking through the filling.

Finish and bake: Top with a final layer of tortillas, then pour over any leftover green chile sauce. Scatter the remaining cheese across the top in an even blanket. Place the dish in the oven and bake for 30–35 minutes. You’re looking for the cheese to melt into a golden, blistered crust—edges should be bubbling and slightly brown, and the whole kitchen will smell of roasted chillies and toasty cheese. Let it rest for 10 minutes before serving; this allows the layers to settle.