Cut pineapples in half lengthwise. Scoop out the flesh using a sharp knife and spoon, leaving about 1/2 inch of border to hold the fillings. Chop the scooped pineapple and set aside. Pat the inside of the shells dry and set them on serving plates.
Season chicken with salt and pepper. Heat oil in a skillet over medium-high heat. Add chicken and sauté until browned and cooked through. Remove and set aside.
In the same pan, add bell pepper, onion, and snap peas. Stir-fry for 3–4 minutes until tender-crisp. Add the chopped pineapple and cook for 1 more minute.
Whisk together all sauce ingredients except cornstarch and water. Bring the sauce to a simmer in the skillet. Stir in the cornstarch slurry and cook until thickened.
Return chicken to the skillet and coat in sauce. Mix with sautéed veggies. Spoon cooked rice into pineapple bowls and top with the teriyaki chicken and vegetables. Serve hot.