In a mixing bowl, whisk together pineapple juice, soy sauce, brown sugar, minced ginger, garlic, and rice vinegar until well incorporated. Set aside half of the marinade for the glaze later. Add the chicken thighs to the remaining marinade, ensuring they're well coated. Cover and let marinate for at least 30 minutes in the refrigerator.

While the chicken marinates, heat a cast iron skillet over medium-high heat. Add a drizzle of oil to coat the bottom evenly. Once the oil shimmers, carefully place the marinated chicken thighs in the skillet, allowing excess marinade to drip off. Sear the chicken for 5-6 minutes on each side, or until they develop a deep golden-brown crust.

In a small saucepan, pour the reserved marinade and bring it to a simmer over medium heat. Allow it to bubble for about 5-7 minutes, stirring occasionally. Stir in the cornstarch slurry gradually until the mixture reaches a syrupy consistency.

Once the chicken is seared golden and cooked through, reduce the skillet’s heat slightly and pour the thickened glaze over the chicken. Cook for an additional 60 seconds, allowing the chicken to soak up the glaze.

Remove the skillet from heat and let the glazed chicken rest for about 5 minutes. After resting, slice the chicken into pieces and transfer to a serving plate. Garnish generously with toasted sesame seeds and thinly sliced green onions.