In a large bowl, whisk the pineapple juice and soy sauce together. Add the brown sugar, ginger, garlic, and rice vinegar. Stir until the sugar dissolves completely. This liquid will give the chicken all its flavor.

Place the chicken breasts into the bowl with the marinade. Cover the bowl and put it in the fridge for 30 minutes. You can leave it longer for a deeper taste. Do not exceed four hours or the meat gets mushy.

Pour half of the unused marinade into a small saucepan. Bring it to a boil over medium heat. Whisk in the cornstarch slurry and simmer for five minutes. The sauce should become thick, glossy, and very dark.

Heat a skillet or grill pan with a little oil. Place the pineapple rings on the hot surface. Grill for three minutes on each side until charred. Remove the fruit and set it aside for later.

Add more oil to the pan if needed. Place the marinated chicken breasts in the hot skillet. Cook for six to seven minutes on each side. The chicken should be golden brown and fully cooked through.

Brush a thick layer of the prepared sauce onto the chicken. Do this during the last two minutes of cooking. This allows the sugar to caramelize without burning. The chicken will look shiny and delicious.

Remove the chicken from the heat and let it rest. Give it about five minutes before you start slicing. This keeps the juices inside so the meat stays tender. Resting is a very important step.

Place a grilled pineapple ring on top of each chicken breast. Drizzle more of the thick glaze over everything. Sprinkle with green onions and sesame seeds. Serve it while it is hot and fresh.