Cut the chicken into 1-inch (2-3 cm) chunks, toss with chili flakes, finely chopped ginger and garlic together, season with salt to taste (but not much, the sauce will be salty). Cook right away or leave to marinate for a minimum of 30 minutes or overnight. (If you’re marinating the chicken for 30 minutes, you can leave it on the counter, if longer - cover the bowl and put it in the fridge, then bring to the room temperature before cooking).
Cut the bell peppers and pineapple into 1/2-inch (1.5 cm) cubes.
Whisk the ingredients for the sauce in a bowl together, set aside.
Cook the rice: rinse the rice, add into a small pot, season with salt, pour in boiling water, cover, and cook over very low heat for about 15 minutes (starting from the moment when it comes to a boil) or until water is absorbed and the rice is soft.
Toss the chicken pieces in potato starch (or cornstarch). Heat the oil in a large frying pan over high heat. Add the chicken to the pan. Cook over high heat for about 2 minutes on each side, until browned, transfer on a plate.
Add bell peppers and pineapple to the pan, cook for about 5 minutes, until lightly browned and tender but still crunchy.
Add the chicken back to the pan, add the sauce, stir everything together, bring to a boil. When the sauce thickens remove the pan from the heat. When using cornstarch you may need to cook the sauce a couple of minutes longer as opposed to potato starch.
Serve with rice, sprinkle with sesame seeds.