Combine the minced garlic, pineapple juice, ketchup, soy sauce, brown sugar, grated ginger, toasted sesame oil, and sriracha (if using) in a bowl and whisk until the sugar is fully dissolved and the mixture is smooth. This creates a balanced sweet-savory-spicy marinade that will develop complex flavors. Add the chicken chunks to a resealable bag or container, pour the marinade over them, and massage gently to coat evenly. Refrigerate for at least 2 hours, or up to overnight—the longer marinating time allows the flavors to penetrate the chicken and tenderize it slightly. I find that marinating overnight gives noticeably more depth of flavor, so plan ahead if you have the time.

While the chicken marinates, core the pineapple and slice it into 1/2-inch thick rings. Lightly brush both sides of each ring with vegetable oil and set aside on a plate. About 10 minutes before you're ready to cook, preheat your grill to medium-high heat (around 400-425°F if using a gas grill). Let it heat for 5 minutes so the grates are hot enough to create good char marks and prevent sticking. The oil on the pineapple will help it caramelize beautifully and prevent it from sticking to the grill.

Remove the chicken from the marinade, allowing excess sauce to drip back into the bag (reserve the remaining marinade for basting). Place the chicken chunks directly on the hot grill grates in a single layer, being careful not to overcrowd the grill. Cook for 8 minutes on the first side without moving them—this allows a flavorful crust to develop. Flip each piece and cook for another 8 minutes on the second side until the internal temperature reaches 165°F when checked with a meat thermometer. I like to brush the chicken with extra reserved marinade during the last minute of cooking to build a glossy, caramelized exterior.

Once the chicken is nearly done, place the oiled pineapple rings on the grill in a single layer. Grill for about 2 minutes per side until you see char marks and the natural sugars caramelize slightly—this brings out the pineapple's sweetness and adds complexity to the dish. Transfer the grilled chicken and pineapple to a serving platter or individual plates. Scatter the sliced scallions over the top as a fresh, aromatic garnish that contrasts beautifully with the warm, caramelized flavors.