Coarsely grate the cucumbers over a paper towel or cheesecloth. Squeeze out as much of the moisture from the cucumbers as possible and add them to a mixing bowl along with the yogurt, vinegar, olive oil, oregano, garlic, ¼ teaspoon salt and ¼ teaspoon black pepper. Stir well to combine, taste for seasoning and adjust with salt, pepper or vinegar as desired. Cover and refrigerate for at least 30 minutes before serving. Leftovers can be refrigerated for up to 5 days.

In a large bowl, combine the pounded chicken, mustard, olive oil, garlic, salt, cumin, oregano, paprika, and black pepper. Toss well to combine, cover and refrigerate 6 hours to overnight.

Preheat your Traeger Grill to 475F.

Assemble your gyros pan by screwing the spit onto the base. Start with half of a large onion, wider side facing up, and proceed to thread the marinated chicken thighs, slightly rotating each one ¼ turn to ensure even cooking.

Place the gyros onto the grill and cook, rotating the pan every 45 minutes, until the chicken is golden brown and the thickest part of the meat registers around 160F, around 1.5 hours. Baste the chicken with the rendered juices, raise the heat of the grill to 500F and cook an additional 10-12 minutes or until the chicken is deeply golden in colour and the thickest part of the meat registers around 180F. Note: if using chicken breast, only cook it until the thickest part reaches 160F.

Remove the gyros from the heat and let it rest 5 minutes before thinly shaving the meat directly off the spit with a sharp knife. Assemble the gyros pitas by spreading a generous layer of tzatziki onto a flatbread, topping it with the shaved chicken, sliced tomato, sliced red onion, a light dusting of smoked paprika, and a pinch of dry oregano. Wrap tightly and serve immediately.