Put the sliced chicken into a large bowl. Add all of the marinade ingredients and combine really well. Cover and let marinate in the fridge at least while you prepare the other ingredients - longer if you can (overnight is ideal).

Pre-heat the oven to 425F/220C and line three baking trays with baking paper (two might be enough if you have one really large one). Also rip or cut squares of baking paper or aluminium foil to wrap the gyros in (foil is easier).

While the oven is heating up, slice the tomatoes and onion and lettuce thinly. Make the tzatziki if making your own (see recipe in notes section below).

Using kitchen tongs or a fork, spread the marinated chicken out on the baking sheet(s). Spread out the frozen fries on the other baking sheet. Bake the chicken and fries for 20 minutes or until the chicken is cooked through, browned and slightly crisp in parts.

Warm the pita bread through either in the oven for a few minutes, or in a pan for a couple of minutes on each side. To assemble, place the pita on the edge of a square of baking paper or foil. Spread a big spoonful of tzatziki down the middle. Add a line of meat, 2 to 3 slices of tomato and onion, and a small handful of lettuce and fries. Sprinkle over a little extra paprika.

To wrap, bring the edges of the pita together, pinching a little more at the bottom to form a cone shape. Roll the gyros up in the paper, tucking the end into the bottom (don't worry if it isn't perfect - it takes a little practice!).