In a bowl or resealable bag, combine the soy sauce, sriracha, freshly minced garlic, ginger, toasted sesame oil, red chili flakes, salt, and pepper. Add the cut chicken thighs and toss to coat evenly, ensuring every piece is well covered with the marinade. I always let the chicken marinate for at least 2-3 hours in the refrigerator—this gives the flavors time to penetrate the meat and keeps it incredibly juicy during grilling. You can marinate up to 8 hours for even deeper flavor development.

While the chicken marinates (or about 15 minutes before you're ready to grill), preheat your grill to medium heat (around 375-400°F). This gives you time to prepare your garnishes and sauces. Mince the green onions and place them in a small bowl. Toast the sesame seeds in a dry skillet over medium heat for 2-3 minutes, shaking occasionally, until fragrant and golden—this deepens their nutty aroma. Have the Japanese BBQ sauce and yum yum sauce ready for serving.

Remove the marinated chicken from the refrigerator and transfer to the preheated grill. Grill for 10-12 minutes total, flipping pieces every 2-3 minutes to ensure even cooking and prevent burning. I like to add the 4 tablespoons of Japanese BBQ sauce during the last 2 minutes of grilling, brushing it onto the chicken pieces as they cook—this creates a beautiful caramelized glaze and locks in authentic flavor. The chicken is ready when it reaches an internal temperature of 165°F. The frequent flipping ensures the bite-sized pieces cook evenly without drying out.

Transfer the grilled chicken to a serving platter. Generously sprinkle the toasted sesame seeds over the top and scatter the minced green onions. Serve with both the Japanese BBQ sauce and yum yum sauce on the side for dipping or drizzling, allowing guests to customize their sauce ratio.