Whisk cornstarch and water together in a small bowl. It will be a milky liquid. This is for thickening the sauce. Combine the cornstarch mixture, brown sugar, honey, soy sauce, vinegar, garlic, ginger, and black pepper together in a small saucepan over low heat. Allow to simmer while whisking occasionally. Bring to a boil and allow to boil for 1 minute. Turn off the heat and set aside for at least 10 minutes, allowing it to cool and thicken.

Meanwhile, preheat oven to 400°F (204°C).

Arrange chicken and pineapple slices in a bake pan (any size works—I used a 10-inch casserole dish. Use a 9-inch square pan, an 11×7-inch pan, an 8-inch square pan, etc). Pour sauce on top, then turn the chicken over to make sure every inch is coated in the sauce. Use a basting/pastry brush if needed.

Bake uncovered for 30–32 minutes or until the chicken is completely cooked through. This is optional: at the 25-minute mark, remove from the oven and carefully slice the chicken into chunks, then return to the oven. The smaller the chicken pieces, the more teriyaki they’ll soak up. You can also cut up the chicken when it is raw prior to cooking.

Sprinkle green onion and sesame seeds on top and serve the chicken and pineapple with sauce from the pan poured on top. Store leftovers in the refrigerator for up to 5 days.