Preheat the broiler. Make the rub: Combine the sesame seeds, lemon zest, thyme, sugar, 1/2 teaspoon salt and 1/4 teaspoon pepper in a spice grinder; pulse until the seeds are slightly cracked. Season the chicken with salt and all but about 1 1/2 tablespoons of the rub. Set skin-side down on a broiler pan and broil, flipping the chicken and rotating the pan halfway through, until the chicken is golden and a meat thermometer registers 170 degrees F, 8 to 10 minutes per side. Make the dressing: Mix 1 tablespoon of the reserved rub, the lemon juice, vinegar, and salt to taste in a bowl. Whisk in the olive oil. When the chicken is done, whisk 1 tablespoon of the pan drippings into the dressing. Add the lettuce, cucumber, tomato and pita chips; season with salt and pepper and toss. Sprinkle the chicken with the remaining 1/2 tablespoon rub and serve with the salad.