Press the chicken thighs between two sheets of baking paper using a rolling pin until they are about 1cm / ½" thick. Place in a baking dish.
Mix all the marinade ingredients together and pour over the chicken. Mix well and leave in the fridge to marinate for 3 hours or even better overnight.
The next day, heat a barbecue or grill pan over high heat. Add a little oil, then the marinated chicken, and cook for 7–8 minutes on each side.
For the flat bread – mix the flour, salt and baking powder in a bowl, then add the yoghurt and mix until a soft dough forms. Leave to rest for 30 minutes, then divide into 6 pieces and roll each into a thin circle. Cook each in a frying pan over a high heat for a minute or two each side. Repeat with the remaining dough. Or, cook on the barbecue.
For the tzatziki - remove the seeds from the cucumber, grate it and put it in a strainer over a bowl. Sprinkle 1 teaspoon of salt on top and leave for 30 minutes to remove the water. Ball and press the garlic, then mix with the yoghurt and the other ingredients.
To make the gyros - spread a spoonful of tzatziki on each flatbread, then top with slices of chicken thigh, chopped tomatoes, cucumber and lettuce. Spread a little more tzatziki on top and garnish with thin slices of red onion.
A recipe originally appeared as part of the Prynhawn Da programme.