In a large bowl, combine olive oil, lemon juice, cumin, coriander, paprika, turmeric, cinnamon, allspice, salt, and pepper. Add the chicken breasts and coat them well with the marinade. Let it marinate for at least 30 minutes.
Heat a grill or skillet over medium heat. Cook the marinated chicken breasts for 6-7 minutes on each side or until fully cooked. Remove from heat and let it rest for 5 minutes before slicing.
To prepare the sauce, mix yogurt and tahini in a small bowl until well combined.
Assemble the tacos by placing slices of chicken into each tortilla. Top with diced cucumber, tomato, red onion, and chopped parsley.
Drizzle the yogurt-tahini sauce over the fillings. Serve immediately and enjoy!