Peel the avocados and remove the stones, then mash the flesh in a small bowl with the back of a fork or potato masher to break it up.
Finely chop the red onion and add to the avocado along with the lime juice, coriander, garlic powder, celery salt and spices. Mix until almost smooth, with some small lumps, then season with salt and pepper.
Quarter, deseed and finely chop the tomatoes, then stir them into the avocado mixture. Add the Tabasco, if using.
Scoop into a serving bowl and arrange on a platter with the selection of raw vegetables.