For the marinade: Combine all ingredients and whisk together. Pour over the chicken thighs in a large ziplock bag and refrigerate at least 1 hour or up to overnight.
Heat the grill. Oil the grill grates. When the grill is ready, place on the chicken thighs, keeping an even layer of marinade, if possible, which will provide caramelization. Grill about 2 minutes, then turn 45 degrees to get grill marks. Grill another 2 min before flipping, then repeat on the other side. This should take about 8 minutes and the thighs should be bare char marks and perfectly cooked through on the inside. About 3 minutes before the thighs are finshed, place the prepared green onions on the grill. Allow the thighs to rest for about 10 minutes then slice against the grain.
To build a wrap, open a lettuce leaf. Place in a bit of chicken, fresh cilantro, grilled green onions and top it off with a generous amount of Sriracha.