Preheat oven to 400 degrees F. Lightly grease a large baking dish.
Prep peppers: halve lengthwise, remove seeds and membranes. Brush inside and outside with olive oil. Season inside with salt and pepper. Place cut-side up in the baking dish.
Make filling: in a large bowl, combine rice, chicken, pineapple, teriyaki sauce, soy sauce, sesame oil, garlic powder, ginger powder, and half the scallions. Stir to combine. Taste and adjust seasoning.
Fill peppers: spoon filling generously into each pepper half, mounding slightly above the rim. Press lightly to compact.
Bake covered: cover dish tightly with foil. Bake 20 minutes.
Bake uncovered: remove foil. Add cheese if using. Bake 10 to 12 more minutes until peppers are tender and filling edges are lightly caramelized.
Serve: rest 5 minutes. Drizzle with extra teriyaki sauce, top with remaining scallions and sesame seeds.