In a large bowl, combine all the marinade ingredients.
Add the sliced chicken (or beef/lamb) to the bowl and mix well to coat the meat evenly.
Cover and refrigerate for at least 2 hours or overnight for best results.
Preheat a grill, skillet, or oven to medium-high heat.
Grill or cook the marinated meat for about 5-7 minutes on each side, or until fully cooked and slightly charred. If using an oven, cook at 400°F (200°C) for about 20-25 minutes.
Slice the cooked meat into thin strips.
In a small bowl, mix together the mayonnaise, yogurt, minced garlic, lemon juice, and olive oil.
Season with salt to taste.
Warm the pita or flatbreads slightly.
Spread a layer of garlic sauce on each bread.
Add the cooked shawarma meat.
Top with shredded lettuce, sliced tomatoes, cucumbers, and red onions.
Roll up the pita or flatbread to enclose the fillings.
Enjoy your meal!