In a large bowl or jug, whisk together the pineapple juice, soy sauce, brown sugar, ketchup, vinegar, Worcestershire sauce, garlic, ginger, neutral oil, sesame oil, and black pepper until the sugar is mostly dissolved. Measure out about 120ml, roughly a quarter of the mixture, into a small saucepan and set it aside. Pour the remaining marinade over the 900g of chicken thighs in a bowl or zip bag and coat every piece thoroughly. The mixture should taste strongly sweet, salty, and acidic at this point, since it mellows with cooking. That reserved portion is what keeps the finishing glaze clean, because it never touches raw chicken.

Cover the bowl or seal the bag and refrigerate the chicken for 2 hours, turning it once if you can so both sides stay in contact with the liquid. If your schedule demands it, the chicken can stay up to 8 hours, but not much longer. After that point the pineapple juice begins to soften the surface of the meat too much, leaving it slightly mushy instead of springy. That shorter window is what gives the thighs real flavour without losing their bite.

Rinse the 300g of rice under cold water until it runs mostly clear, then drain well. Combine it in a pot or rice cooker with the water, using 450ml for jasmine and up to 500ml for a firmer medium grain, plus the ½ tsp salt. Bring a pot to a boil, cover tightly, and cook on low for about 12 minutes until tender, or follow your rice cooker. Keep it covered off the heat for 10 minutes before fluffing. That covered rest is what lets the grains finish steaming evenly, so they stay fluffy and separate rather than wet or compacted.

Place the saucepan with the reserved clean marinade over medium heat and bring it to a simmer. Cook for 6–10 minutes, stirring occasionally, until the sauce turns glossy and lightly thickened and coats the back of a spoon while remaining pourable. If it reduces too far, loosen it with 1–2 tsp water. It will thicken a little more as it cools, so stop while it still flows. That restraint is what keeps the glaze clinging to the chicken instead of setting into candy.

Lift the chicken from the marinade and let the excess drip off, so the pieces are coated but not dripping wet. Grill over medium-high heat, or cook in a grill pan or heavy skillet, for about 5–7 minutes per side depending on thickness. During the last few minutes, brush with some of the reduced glaze and turn once or twice to build a lacquered finish. Cook until the thickest piece reaches 74°C / 165°F, then rest on a plate for 5 minutes. That order of char first and glaze last is what gives a sticky finish without burnt sugar.

While the chicken rests, grill or sear the pineapple chunks for 1–2 minutes per side until lightly caramelised with dark golden spots. Brush very lightly with the neutral oil only if the pieces stick to the grates or pan. Keep the chunks intact and juicy, pulling them as soon as the edges colour rather than cooking them until limp. That short, hot contact is what concentrates the sweetness while preserving the fresh pineapple character against the savoury chicken.

Slice or chunk the rested chicken into large bite-size pieces, then divide the fluffy rice among 4 bowls. Top each bowl with the chicken and several grilled pineapple chunks, about one quarter of each per serving. Spoon a little extra glaze over the chicken and let a small amount run onto the rice, leaving a modest glossy pool rather than a drenching. Finish with the sliced scallions and toasted sesame seeds just before serving. That late garnish is what keeps the scallions fresh and crisp against the warm, sticky chicken.