Add the rice and water to a medium size saucepan and bring to a boil over medium-high heat. Cover pan tightly and reduce heat to low. Cook on low for 10 minutes (DO NOT REMOVE THE LID) then turn off the heat and let rest 15 minutes (Once again, DO NOT REMOVE THE LID).
Place the chicken and cornstarch in a bowl and toss to coat, set aside for 10 minutes.
Heat the oil in a wok or large nonstick skillet over medium-high heat. When oil is hot add the chicken and stir-fry until chicken is cooked through, about 10 minutes. Transfer cooked chicken to a plate and set aside.
Add the serrano pepper and bell pepper to the pan and cook, stirring often, until the peppers begin to soften, about 3 minutes.
Add the garlic and ginger to the pan and cook until fragrant, about 10 seconds. Add the mango chunks and peanuts. Cook, stirring occasionally, about 2 minutes.
Add the soy sauce, vinegar, red pepper flakes and the chicken into the pan. Stir and cook until heated through, about 2 more minutes. Serve over the steamed rice.