In a bowl, stir together warm water, brown sugar, orange juice, soy sauce, ketchup, white vinegar, garlic, red pepper flakes, five-spice powder, and orange peel until the sugar has dissolved and the mixture is well combined.
Heat the olive oil in a large skillet or wok over medium heat, and cook and stir the chicken until the outside is golden brown and the inside is no longer pink, 10 to 12 minutes. Pour the sauce mixture over the chicken, bring to a boil, reduce heat to medium-low, and cover the skillet. Simmer for 30 minutes, stirring occasionally.
While the chicken and sauce are simmering, bring the rice and water to a boil in a saucepan over high heat. Reduce heat to medium-low, cover, and simmer until the rice is tender, and the liquid has been absorbed, 20 to 25 minutes. Set the rice aside and keep warm.
Whisk the cornstarch and 2 tablespoons of cold water in a small bowl until smooth, and stir into the chicken and sauce, a few teaspoons at a time. Let the chicken and sauce cook for about 2 minutes to thicken, then serve over hot cooked rice, sprinkled with green onion.
