Warm sesame oil in a small saucepan over medium heat until shimmering. Sauté the ginger and garlic for roughly 1 minute, or until aromatic. Pour in the soy sauce, vinegar, brown sugar, ketchup, and smoked paprika, stirring to integrate.

In a separate bowl, dissolve cornstarch in ¼ cup of cool water to create a slurry. Incorporate this mixture into the saucepan and stir thoroughly. Elevate the heat to bring the sauce to a gentle boil, then reduce to medium-low. Simmer for 3–4 minutes, until the sauce thickens enough to coat the back of a spoon. Take off the heat.

Set aside ½ cup of the prepared sauce in a small bowl. Pour the remaining marinade into a large bowl and allow it to cool slightly, about 5 minutes. Add the chicken thighs and toss until evenly coated.

Preheat a grill or grill pan over medium-high heat. Lightly grease the grill grates with vegetable oil. Arrange the marinated chicken on the grill, cooking each side for 4–6 minutes. Baste with half of the reserved sauce, flip, and continue grilling for another 2–4 minutes. Finish with a final brush of the remaining sauce and grill for 2 additional minutes. The chicken is done when a thermometer inserted into the thickest part reads 165°F. Transfer to a serving platter.