Halve the avocados, remove the stones. Lift the flesh of an avocado out of the shell and puree in a bowl. Add the chopped tomato, the tuna meat chopped into small pieces, the finely chopped onion and the chopped eggs, season with salt, pepper and lemon juice. Mix in a little olive oil to create a creamy farce. Fill the pitted avocados with this farce, sprinkle with chopped herbs and serve with toasted white bread.