How to Make It
Preheat grill to high. Combine chicken, mint, garlic, 1/3 cup oil and 1 tsp. salt in a ziplock bag. Toss to coat. Let stand while grill heats.
Whisk together tahini, lemon juice, remaining 2 Tbsp. oil and remaining 1/2 tsp. salt in a small bowl until smooth. Whisk in water, 1 tablespoon at a time, until mixture has thinned to the consistency of sour cream. Sprinkle with sesame seeds, if desired.
Thread chicken on skewers and grill with cover closed, turning once, until cooked through, 6 to 8 minutes total. Serve with tahini sauce on the side.