For the easiest process of cooking with little mess, cut chicken thigh into cubes.
Place chicken thigh cubes in a large ziploc bag. Add oil, garlic, lemon juice, and all of the spices into the bag
Close the ziploc bag and mix well by shaking the bag until all spices are well incorporated. Refrigerate the marinated chicken for at least one hour, best if done over night.
Set InstantPot on to saute mode, add 1/4 cup of oil into pot and diced onions. Cook until they become translucent golden brown. Hit the cancel button to turn off InstantPot.
Add in marinated chicken into the InstantPot. Close lid with vent pointed to sealed. Set Manual for 8 minutes and leave chicken to cook.
Allow the pot to natural release the steam, approximately letting it sit for at least 10 minutes before releasing the vent.
Open lid of InstantPot. Turn on saute mode, stirring the chicken so it does not stick to the bottom of the pot, but allowing most of the liquid to evaporate. Feel free to using a wooden spoon separate the cubes of chicken into shreds. Alternatively, you may chop the chicken on a cutting board into thinner slices
Once liquid has evaporated, chicken shawarma is complete.
Assemble your sandwich by cutting a large pita bread in half around the perimeter so you have two equal sized flat circles. Place some of the chicken in the center of one of the slices of bread, in a long line to span the width of the bread. Add any of your preferred condiments, traditionally it is filled with garlic sauce, sliced pickles, or sometimes can be filled with tahini sauce instead if you don’t prefer garlic. Roll this bread filled with chicken, it may tear but continue to gently roll it. Place this rolled bread on top of the second slice of pita, roll delicately from one side to the next until you have completely rolled the pita into a classic shawarma shape. Place into a Panini press or George Foreman grill for 3-5 minutes to grill the exterior of the bread. Noshejaan!