Cut the block of mozzarella into 30 sticks; season them with salt and pepper. Dredge them in flour, shake off the excess, dip them in the beaten egg whites, and finally coat them in breadcrumbs. Let them rest in the refrigerator for at least 1 hour.
Grate the cucumber using the coarse side of the grater, season with salt, and let it drain in a sieve for 20 minutes. Squeeze it out a bit and add the yogurt, along with a good half of the chopped dill, the pressed garlic cloves, salt, and pepper.
Fry the croquettes until golden brown in the deep fryer at 180°C. Let them drain on kitchen paper.
Divide the tzatziki among glasses, add the croquettes, garnish with dill, and serve.
Tips
Do not bake too many croquettes at the same time, so you avoid that the temperature of the oil suddenly drops, making the result less crispy.