Heat a small saucepan over medium heat and add the minced garlic and grated ginger, cooking for about 2 minutes until fragrant. Pour in the soy sauce, water, brown sugar, mirin, and rice vinegar, stirring to combine. Bring the mixture to a boil, then reduce heat and simmer for 4 minutes to allow the flavors to meld. Remove from heat and let cool to room temperature. I find that letting the sauce cool completely before using it on the chicken prevents the exterior from cooking too quickly and unevenly.

While the sauce cools, soak wooden skewers in water for at least 15 minutes to prevent burning on the grill. Cut the chicken tenderloins into 1-inch cubes and thread them evenly onto the skewers, leaving a small gap between pieces for even cooking.

Stir the cornstarch slurry (cornstarch mixed with water) into the cooled teriyaki sauce until fully combined—this will thicken the glaze so it clings beautifully to the chicken rather than running off. Preheat your grill to 350°F, ensuring the grates are clean and lightly oiled to prevent sticking.

Place the chicken skewers on the preheated grill and sear for 1 minute on each side to develop a light golden crust. Then begin basting generously with the thickened teriyaki sauce from Step 3, flipping the skewers every minute and re-coating with sauce. Continue this process for 8-10 minutes total, until the internal temperature reaches 165°F when checked with a meat thermometer. I like to add the toasted sesame oil to the sauce in the final 2 minutes of cooking—this keeps its delicate nutty flavor from being lost to the heat.

Transfer the grilled chicken skewers to a serving platter and give them one final brush of the teriyaki glaze. Top with the thinly sliced scallions and toasted sesame seeds, then serve immediately while still warm.