Place the chicken thighs in a bowl or zip-lock bag with the lemon juice, olive oil, cumin, salt and pepper.Cover or seal and refrigerate for at least an hour, or overnight.
Heat a drizzle of oil in a skillet over medium-high heat and cook the chicken for 8-10 minutes, until browned and cooked through. Transfer to a cutting board and slice.
Whisk together the tahini, yogurt, lemon juice, olive oil, garlic and a pinch of salt.
Assemble the salad on a large platter or in individual shallow bowls, with chopped romaine, diced tomatoes, cucumbers, purple onion, olives and parsley.
Top with the chicken and drizzle with tahini dressing.