Step 1

Pulse garlic, egg whites, and lemon juice in a food processor until smooth. With motor running, very gradually stream in half of the oil (this will help the emulsion stay together). Scrape down sides of processor and continue to process, gradually adding remaining oil, until mixture thickens and becomes light and airy (it should cling to a spoon). Season with salt.

Step 2

Do Ahead: Toum can be made 2 days ahead. Cover and chill.

Step 3

Mix lemon juice, tomato paste, coriander, 1/4 cup toum, and 3 Tbsp. oil in a large bowl to combine. Transfer marinade to a large resealable plastic bag. Save remaining toum for serving.

Step 4

Working one at a time, slice chicken thighs in half lengthwise and season generously with salt. Add to bag with marinade, seal bag, and massage marinade into chicken. Chill at least 3 hours and up to 12 hours.

Step 5

Let chicken sit at room temperature 1 hour before grilling.

Step 6

Prepare a grill for medium heat; oil grate. Thread chicken onto skewers, folding pieces back and forth accordion-style so they pile onto themselves (it should be about 3 strips per skewer). Grill, turning occasionally, until browned and beginning to char in spots, 10–12 minutes.

Step 7

Serve chicken on top of pitas, with pickles and reserved toum alongside