Place all the chimichurri sauce ingredients in a food processor or blender and blend until fairly smooth. Season to taste and set aside until required.
Brush the steaks with a little oil and season liberally with salt and pepper. Cook on a hot barbecue for 3—4 minutes on each side or until cooked to your liking. Set aside to rest for 3 minutes.
Meanwhile, make the salsa. Put the avocado, tomatoes, chilli, coriander, lime juice and some salt and pepper in a bowl and mix well.
Serve the steaks topped with the salsa and drizzled with the chimichurri sauce.