Flatten the chicken — Place each thigh between two sheets of baking paper or cling wrap and pound to an even thickness of about 1.5–2 cm using a meat mallet or rolling pin.

Make the marinade — In a large bowl, combine the yogurt, lemon juice, and souvlaki seasoning. Mix until smooth.

Marinate — Add the flattened thighs, turning to coat all sides. Cover and refrigerate for at least 2 hours, or overnight for best results.

Preheat oven to 180°C (356°F).

Skewer the chicken — Place an onion half cut-side down as a stable base. Thread the thighs lengthwise onto both skewers side by side so they lie flat and don’t spin. The onion anchors the base.

Bake — Place in a baking dish or lined tray. Bake for 1 hour, turning halfway, until golden and cooked through (internal temp 75°C / 165°F).

Rest and slice — Rest for 5 minutes, then slide off the skewers and slice or tear into pieces.

Make the tzatziki — Squeeze all moisture from the grated cucumber using a clean towel. Combine with yogurt, garlic, lemon juice, olive oil, dill, salt, and pepper. Mix well, taste, and adjust seasoning. Refrigerate for at least 30 minutes before serving.

Assemble — Warm the pita. Top with chicken, sliced tomato, julienned red onion, and a generous spoonful of tzatziki. Serve with chips or fries on the side.