In a large bowl, combine 1 cup of plain yogurt, 2 teaspoons of lemon juice, 4 minced garlic cloves, 1/2 teaspoon of hot pepper sauce, 1 teaspoon of vinegar, 1 teaspoon of minced onion, 1/2 teaspoon of black pepper, 1/2 teaspoon of cayenne pepper, 1/2 teaspoon of ground mace, and 1/2 teaspoon of salt.
Add 2 sliced chicken breasts to the marinade and mix well.
Cover and marinate the chicken in the refrigerator for at least 12 hours, stirring occasionally.
Grill the marinated chicken until fully cooked, or broil in the oven.
In a separate bowl, combine 1 cup of tahini, 2 minced garlic cloves, 2 teaspoons of lemon juice, and 2 teaspoons of chopped parsley.
Whisk the tahini mixture well, adding 1/2 cup of water if needed to achieve desired consistency.
To assemble the shawarma sandwich, slice open a pita bread and spread some tahini sauce on it.
Add sliced lettuce, mixed sprouts, sliced tomato, and sliced onion to the pita.
Place the cooked chicken on top of the vegetables.
Drizzle a little tzatziki sauce over the sandwich and enjoy.