Peel the garlic, then bash in a pestle and mortar with the cumin, fennel seeds and a good pinch of sea salt to make a paste.
Stir in the chilli flakes, paprika and the juice from 1 lime, then loosen with a good drizzle of olive oil.
With a sharp knife, score the skin of the herring at 1cm intervals, being careful not to cut into the flesh. Spoon the rub over the fish and gently push into the slits. Place the fillets on a baking tray, skin-side up, and set aside.
For the guacamole, halve and destone the avocados and scoop the flesh into a mortar, reserving the skins. Don’t bother washing the pestle and mortar first – the flavours from the rub will only make the guacamole taste better.
Squeeze in the lime juice, pick, roughly chop and add the coriander leaves, then smash it all together. Season, then spoon back into the avocado skins and chill until ready to serve.
For the salsa, roughly chop the tomatoes, coriander leaves and chilli on a board, mixing them together as you go. Add a tiny pinch of salt and black pepper and a splash of extra virgin olive oil. Keep running your knife through it until all the flavours are mixed together.
Heat your griddle pan over a high heat so it’s screaming hot.
Mix the yoghurt and juice of 1 lime together. Line up your taco shells, fillings and greens so you’re ready for the fish.
When the pan is hot, pop on the fillets for a couple of minutes, or until the skin is beautifully crisp and the flesh cooked through. Serve up with the gem lettuce and some mixed cress, if you like, and let everyone dig in!