Rinse the rice until the water runs mostly clear. Combine it with 1 1/2 cups water and the optional salt in a saucepan, bring to a boil, cover, reduce the heat to low, and cook for 15 minutes. Remove from the heat, let stand covered for 10 minutes, then fluff with a fork.

Heat the oven to 375°F (190°C) and lightly grease a 12-cup muffin pan. Press one wonton wrapper into each cup with the corners pointing upward. For sturdier cups, bake the empty wrappers for 4–5 minutes before filling.

Heat the neutral oil in a large skillet over medium-high heat. Add the ground chicken, garlic, ginger, and black pepper, then cook for 6–8 minutes while breaking up the meat, until no pink remains and the chicken reaches 165°F (74°C).

Stir in the teriyaki sauce, optional rice vinegar, and diced pineapple. Cook for 2–3 minutes, until the mixture is hot and slightly thickened, then remove the skillet from the heat and stir in the green onions.

Spoon approximately 1 1/2 tablespoons of filling into each wonton cup, taking care not to overfill them. Bake for 8–10 minutes, until the wrapper edges are crisp and golden brown.

Sprinkle the baked wontons with sesame seeds and additional green onion. Serve immediately with the steamed rice and drizzle with extra teriyaki sauce if desired.