In a large bowl, whisk together honey, soy sauce, minced garlic, grated ginger, and rice vinegar until well combined.
Add the chicken thighs to the marinade, ensuring they are fully coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Heat vegetable oil in a large skillet over medium-high heat. Remove chicken from the marinade, allowing excess marinade to drip off, and season with salt and pepper.
Place the chicken in the skillet and cook for about 5-7 minutes on each side, or until the chicken is golden brown and cooked through.
While the chicken is cooking, pour the remaining marinade into a small saucepan. In a separate bowl, mix cornstarch and water to create a slurry, then add it to the saucepan.
Bring the marinade to a boil over medium heat, stirring constantly until it thickens. Remove from heat.
Once the chicken is cooked, pour the thickened sauce over the chicken in the skillet, tossing to coat evenly.
Serve hot, garnished with chopped green onions if desired.