Make the huli huli sauce. Heat the sesame oil in a small saucepan over medium heat. Once the oil is glistening, add the ginger and garlic and cook, stirring, until fragrant, about 1 minute. Stir in the soy sauce, rice vinegar, brown sugar, ketchup, and paprika until combined.

In a small bowl, whisk the cornstarch with ¼ cup cool water to form a slurry. Add the cornstarch mixture to the saucepan, and stir to combine. Bring to a boil, then reduce the heat to medium-low and simmer, stirring occasionally, until the sauce is thick enough to coat the back of a spoon, 3 to 4 minutes. Remove from the heat.

Transfer ½ cup of the sauce to a small bowl and set aside for basting. Transfer the remaining marinade to a large bowl and let cool for 5 minutes. Add the chicken thighs and toss to coat.

Heat a gas grill or grill pan to medium-high. Brush the grates with vegetable oil to prevent sticking. Remove the chicken from the marinade, discarding the used marinade. Place the chicken on the grill and cook for 4 to 6 minutes per side.

Brush the chicken with half of the reserved sauce, then flip and cook for 2 minutes. Brush with the remaining sauce and cook for 2 more minutes, until the internal temperature reaches 165°F on an instant-read thermometer and the exterior is caramelized and charred in spots.

Transfer the chicken to a large platter, and serve warm.