Peel and take out the seeds . Cut the cucumber in 20 sticks of around 6 cm long, then put in the fridge.
Cut the chilly and the rest of the cucumber in big squares, mix it with the onion and the garlic. Then, add the white bread, the vinegar, the olive oil and the salt, with a little bit of chilly. Mix 2 or 3 minutes and find the consistance you like. Or the one you are looking for by adding between 20 and 50 cl of water. Leave it like this in the fridge at least 2hours. To make the cucumber better, add the yogurt, a little bit of vinegar and the chopped tarragon.
Mix the gaspacho until it becomes foamy. And pour into a glass or a big plate, put in the middle the cucumber sticks and the yogurt sauce. Serve the gaspacho very fresh.