Approximation of street food I've never had, so can't really speak to the authenticity, but it's good. This was for 3 people, scale accordingly.
1 lb of boneless skinless chicken thighs
1/2 of a medium yellow onion
Tzatziki sauce (we use Cedar's brand, or you can make your own at the link below but why)
Pita bread (we use Stonefire Naan instead)
Romaine (or any lettuce)
Cherry tomatoes (or any tomatoes)
Cucumber (or not, if you forgot to buy it)
Marinade (approximations, eyeball it):
~ 1 tsp of minced garlic from the jar
1/2 lemon's worth of juice
~ 1 Tbsp of Harissa Spice blend
~ 2 or 3 Tbsp of olive oil
Marinate the chicken in those 5 things for 2 hours, or as long as you can stand to wait, up to overnight. Thin-slice the onion and add it to the marinade and stir to coat. Spread chicken + onion mix on a greased sheet pan with the onions tucked under the chicken as much as possible to prevent scorching at the edges. Add more harissa spice if the chicken pieces look too naked. Cook for 30 minutes at 425°F. Slice chicken and serve on warmed pita bread with chopped romaine, halved cherry tomates, sliced cucumbers, and tzatziki sauce.