Preheat the oven to 375°F (190°C). While it heats, bring a large pot of water to a boil. Cut the tops off the bell peppers and remove the seeds and membranes. Blanch the peppers in boiling water for 3 minutes, then drain and set aside.

In a large skillet, heat the olive oil over medium-high heat. Add the diced onion and cook for 2 minutes until translucent. Add the diced chicken, season with salt and pepper, and cook until golden brown and cooked through, about 5-7 minutes. Stir in the garlic and ginger, cooking for another 30 seconds until fragrant.

Pour in the pineapple chunks and cooked rice, then add the teriyaki sauce. Stir everything together and let it simmer for 2 minutes, allowing the flavors to meld. The mixture should be thick and sticky. Taste and adjust seasoning if needed.

Place the blanched peppers upright in a baking dish (if they wobble, trim a thin slice off the bottom). Spoon the chicken and rice filling into each pepper, pressing gently to pack it in. If using cheese, sprinkle it on top now.

Cover the dish with foil and bake for 20 minutes. Then remove the foil and bake for another 10 minutes, until the peppers are tender and the tops are slightly caramelized.

Let the peppers cool for 5 minutes before serving. Garnish with fresh cilantro if desired. Drizzle any extra teriyaki sauce from the pan over the top.