Chop each chicken breast into 8 bite-sized chunks then place in a large bowl.
Add all the marinade ingredients, mix well and allow to marinade for at least 30 minutes but up to 24 hours, covered in the fridge.
30 minutes before cooking, soak bamboo skewers in boiling water.
To make the tzatziki, place the zucchini in a fine mesh strainer and sprinkle over 1 teaspoon salt. Massage the salt into the zucchini and allow to drain for 10 minutes. Squeeze out the rest of the liquid and place in a bowl. Add the remaining tzatziki ingredients and mix well. Set aside.
When you are ready to cook the chicken, thread the chicken onto the soaked skewers. Preheat a grill until hot then cook the chicken for 3-4 minutes per side until golden brown all over and cooked through. Remove from the heat and allow to rest for 5 mins.
Serve the cooked chicken souvlaki with the tzatziki, salad and warmed pita breads (optional).