Steps
1. In a bowl, combine olive oil, lemon juice, oregano, garlic, salt, and pepper. Add chicken cubes and marinate for at least 30 minutes.
2. While the chicken marinates, prepare the tzatziki: mix grated cucumber, yogurt, dill, and a pinch of salt in a small bowl. Set aside.
3. Preheat a grill or grill pan over medium-high heat. Thread chicken onto skewers.
4. Grill chicken skewers for about 10-12 minutes, turning occasionally, until they are cooked through.
5. Warm the pita bread on the grill for a minute on each side.
6. Serve the grilled chicken on the pita, with tzatziki sauce and garnish with lettuce and tomato.