Step 1

Heat the oven to 200C/180C fan/gas For the marinade, tip the onion and garlic onto a small baking tray, and toss with 1 tsp of oil. Roast for 20 mins until golden.

Step 2

Meanwhile, heat a dry frying pan over a medium-high heat and toast the ground spices for 1-2 mins or until fragrant. Peel the roasted garlic and transfer to a food processor along with the onion, toasted spices and all the remaining marinade ingredients, plus 15g of salt. Blend until it forms a smooth paste. Set aside.

Step 3

Make the avocado purée by blending all the ingredients with 10g of salt and 50ml of water to a smooth paste. Season. For an even smoother paste, pass through a fine-mesh sieve.

Step 4

Turn down the oven to 180C/160C fan/gas Coat the fish in most of the marinade, season with salt and white pepper, and marinate for 1 hr. Line a deep baking tray with the banana leaves, leaving the long edges overhanging each side. While the fish marinates, make the filling by combining all the ingredients in a large bowl with the left-over marinade. Arrange the fish over the banana leaves and spoon the filling into the cavity. Enclose the fish using the overhanging banana leaves, trying not to leave any holes. Bake for 25 mins until cooked through – pull away a small part of the fish to make sure it is opaque and flaky. If not, cook for a few minutes more.

Step 5

Serve the fish inside the banana leaves, alongside the corn tortillas, plenty of lime wedges and the avocado purée.