Put the orange juice, ketchup, brown sugar, vinegar, Worcestershire sauce and red pepper flakes in a medium saucepan, and bring to a boil over high heat. Reduce the heat to low and simmer, stirring occasionally, until thick, about 15 minutes. Keep about 1/2 cup warm for serving and set aside the rest for glazing.
Preheat the grill to high heat. Brush the chicken with oil on both sides and sprinkle with salt and pepper. Grill smooth-side down, covered, until lightly charred, 3 to 4 minutes. Flip and brush generously with the glaze. Cook, covered, until charred and the thighs are just cooked through, another 3 to 4 minutes. Flip again, glaze, and cook uncovered about 1 minute. Remove the chicken to a cutting board, sprinkle with the chives if using, and rest the chicken for a few minutes.
Slice the chicken into thin strips. Serve with butter lettuce leaves for wraps and the reserved glaze on the side.