For the tomatillo sauce, place the coriander (leaving the stalks on) in boiling salted water for 15 seconds, then remove and place in a bowl of iced water. Strain off water and dry the coriander on paper towels. Place the coriander, tomatillo purée, onion, epazote and chilli in a high-speed blender and process until the mixture thickens (the seeds break down and act as a thickener). Season with salt to taste and set aside. For the marinade, place the orange juice and achiote paste in a high-speed blender and process until thoroughly combined and slightly thickened. Remove the shells of the prawn cutlets, devein and slice up the middle. Combine the prawns and orange juice mixture in a bowl, cover, and refrigerate for 2 hours. For the guacamole, mash the avocados in a bowl with a fork, then add the chilli, onion, garlic and coriander, and mix well. Add the tomato, lime juice and Tabasco and salt to taste. Set aside. Drain the prawns, reserving the marinade. In a frying pan, heat the olive oil until it shimmers, place the drained prawns in the frying pan and fry until cooked, then add the orange juice marinade. Remove the prawns and reduce the liquid until thick enough to coat the prawns. Return the prawns to the pan, remove from the heat and set aside. Fill the taco shells with guacamole followed by spring onion, coriander leaves, then prawns. Serve with tomatillo sauce on the side. SIMON SAYS: If you can’t get serrano chilli, jalapeño can be substituted. You can find all the specialty Mexican ingredients at www.mexicanspecialities.co.nz.