Step 1

Combine onion and lime juice in a bowl and stand for about 30 minutes. Just before serving, place the onion mixture in a food processor with the avocado, cumin, coriander and chilli, then pulse to form a coarse puree. Season well.

Step 2

To make the fajitas: Combine cumin, paprika, oregano, lime juice, 1 tablespoon oil and some salt and pepper in a bowl.

Step 3

Add the steak, then stand at room temperature to marinate for up to 15 minutes.

Step 4

Heat the remaining tablespoon of oil in a large frypan over medium-high heat, then add the capsicum and onion. Cook, stirring, for 2-3 minutes until softened.

Step 5

Remove from the frypan and keep warm. In 2 batches, add the steak to the pan and cook, turning, for 2-3 minutes until brown and just cooked.

Step 6

Remove from heat, then return the vegetables to the pan and stir through the coriander.

Step 7

Fill the tortillas with steak mixture, top with sour cream and guacamole, and serve with lime wedges.