With a sharp knife, cut the cold tuna fish into nice, even cubes.
Squeeze the juice of the lime and mix it together with the tuna fish. Let it rest for about 5 minutes.
Dice the chili, the cucumber and the celery into small cubes, and finely chop the coriander. Mix the veggies together with the pumpkin seed pesto and the marinated tuna fish, and flavor it mildly with some Fleur de Sel.
Place it on a plate, and garnish it with the quartered, pitted and peeled avocado.