Use a large knife to pulverise 1 large ripe tomato to a pulp on a board, then tip into a bowl.
Halve and stone the 3 avocados (saving a stone) and use a spoon to scoop out the flesh into the bowl with the tomato.
Tip the juice of 1 large lime, a handful of roughly chopped coriander, 1 finely chopped small red onion and 1 deseeded and finely chopped red or green chilli into the bowl, then season with salt and pepper.
Use a whisk to roughly mash everything together. If not serving straight away, sit a stone in the guacamole (this helps to stop it going brown), cover with cling film and chill until needed.