Preheat your oven to 375°F (190°C).
In a large skillet, heat the olive oil over medium heat. Add the diced onion and garlic, sautéing until the onion is translucent, about 3-4 minutes.
Add the ground chicken to the skillet, cooking until browned and fully cooked, about 5-7 minutes.
Stir in the cooked rice, diced pineapple, teriyaki sauce, black pepper, and salt. Cook for an additional 2-3 minutes until everything is heated through.
While the filling is cooking, slice the tops off the bell peppers and remove the seeds.
Place the bell peppers upright in a baking dish. Spoon the chicken and pineapple mixture into each pepper, packing it down gently.
Cover the baking dish with aluminum foil and bake for 25 minutes.
Remove the foil and bake for an additional 10 minutes, until the peppers are tender.
Garnish with chopped green onions before serving.