Preheat the oven to 190°C (170°C fan). While it heats, warm the olive oil in a small frying pan over a medium heat. Add the diced onion and cook for 4–5 minutes, until it turns translucent and releases a sweet, savoury aroma. You'll know it's ready when the edges just begin to brown.

Prepare the creamy filling. In a large mixing bowl, combine the shredded chicken, drained green chiles, sour cream, chicken stock, cumin, garlic powder, onion powder, and a generous pinch of salt and pepper. Stir everything together until the mixture looks uniformly pale green and smells fragrantly of cumin and chiles.

Begin layering the casserole. Spread a thin layer of the chicken mixture (about 4 tablespoons) across the bottom of your 9x13 inch baking dish. This prevents the tortillas from sticking. Arrange 4 tortillas over the sauce, tearing them to fit if necessary, so they cover the base completely.

Add the first full layer. Spoon half of the remaining chicken mixture over the tortillas and spread it evenly with the back of a spoon. Sprinkle one-third of the grated cheese over the top. You should see a thick, creamy layer dotted with flecks of green chile.

Repeat the layers. Place another 4 tortillas on top of the cheese, pressing down gently. Spread the rest of the chicken mixture over these tortillas, making sure it reaches the edges. The filling should look thick and slightly glossy. Sprinkle another third of the cheese over this layer.

Bake until bubbly and golden. Cover the dish tightly with aluminium foil and bake for 20 minutes. Remove the foil and continue baking for another 10 minutes. The casserole is ready when the cheese on top is melted and bubbling, with golden-brown patches forming around the edges. The filling should be visibly steaming and the tortillas will have softened completely.

Rest before serving. Let the casserole sit on the counter for 5 minutes. This allows the layers to set slightly, so when you cut into it, the slices hold their shape rather than turning into a sloppy pile. Garnish with fresh coriander and lime wedges if desired.