Start with the marinade by combining all the ingredients in a medium bowl and whisk well.
Add the chicken cubes in the bowl of the marinade and refrigerate for 1-2 hours.
Remove from the refrigerator 1 hour prior to cooking and put on skewers.
Set a large grill pan over high heat and let it heat up for 2’. Add the chicken skewers turning frequently for about 10-12’.
In the meantime, prepare the tzatziki by mixing all the ingredients.
Serve the chicken souvlaki next to the tzatziki, some finely sliced onions and tomatoes.