Dice the shallot very finely then let it sit with vinegar for about 10-15 minutes. In the meantime prepare your salad.
Add Extra virgin olive oil, salt and pepper. Mix well.Samin recommends to take a piece of lettuce, pour a bit of vinaigrette on top, taste and then adjust.
For the salad:
Wash tomatoes and cucumber.
Peel the cucumber and slice it (or make ribbons).
Chop the tomatoes.
Cut the avocado in 4 parts.
Cube the feta.
Add cucumber, tomatoes, avocado, feta, olives (to taste) and fresh chives into a bowl.
Season with vinaigrette and toss.
Serve immediately (or store it into the fridge, but eat it ASAP)