Peel and finely chop the onion. Halve the chilli, scrape out the seeds, wash and chop finely. Halve avocados, turn halves against each other, remove the stone. Remove the flesh from the skin and chop finely, sprinkle immediately with lemon juice. Puree with onion and chilli.
Wash, clean and finely dice the tomatoes. Stir into the avocado cream. Season to taste with salt. Keep cool until serving
With 10 people: