Pat chicken breasts dry with paper towels. If breasts are uneven in thickness, place between plastic wrap and gently pound to an even 3/4-inch thickness using a meat mallet.

In a medium bowl, combine pineapple juice, diced pineapple, soy sauce, mirin, sake, brown sugar, garlic, ginger, and sesame oil. Whisk thoroughly until sugar is dissolved.

Place chicken in a resealable plastic bag or glass container. Pour 3/4 of the marinade over chicken, reserving 1/4 cup for the glaze. Ensure chicken is fully coated, then seal and refrigerate for 2-4 hours (no longer than 4 hours as pineapple enzymes can make the chicken mushy).

Remove chicken from refrigerator 30 minutes before cooking to allow it to come to room temperature. Preheat oven to 375°F. Remove chicken from marinade and pat lightly with paper towels to remove excess moisture.

Heat a cast-iron skillet over medium-high heat until very hot. Add 1 tablespoon of neutral oil with a high smoke point. Place chicken in skillet and sear undisturbed for 3 minutes until deep golden brown.

Flip chicken, transfer skillet to preheated oven, and cook until internal temperature reaches 165°F, approximately 7-9 minutes depending on thickness. Use a digital thermometer for accuracy.

Remove chicken from skillet and transfer to a plate. Tent loosely with foil and rest for 7-10 minutes to allow juices to redistribute.

While chicken rests, pour reserved marinade into a small saucepan. Bring to a simmer over medium heat. In a small bowl, whisk together cornstarch and cold water to create a slurry. Add to simmering marinade and whisk constantly until mixture thickens to a glossy glaze, about 1-2 minutes. Stir in honey for added shine and sweetness.

Slice chicken against the grain, drizzle with glaze, and garnish with sliced green onions, toasted sesame seeds, and additional pineapple chunks if desired.