Place chicken thighs in a ziploc bag and pound out until fairly flat. Rub tomatillo salsa on both sides, the longer you let the marinade, the better the flavor.
Take stem out of poblano and slice, slice onion. Drizzle with olive oil and grill till tender.
Grill chicken for about 10 min each side till done.
Heat one side of pita, flip, add chicken, veggies and cheese. Place grated cheese, grilled veggies, a little more cheese, the chicken, then brush or spoon on a generous amount of tomatillo salsa, then a little more cheese then top with other pita and flip. Grill till cheese melts.