Wash the chicory leaves well, if necessary put them in water for 10 minutes, then they are not so bitter. Spread on a plate or tray so that they can be filled easily.
Slice the avocado, place the pulp in a small bowl and mash it with a fork. Add the tuna with some of the juice. Also the lemon juice (so that the avocado doesn`t turn gray). Mix everything well. Season to taste with salt and pepper. Spread on the chicory leaves.