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 everything is well combined. Set aside.

Heat olive oil in a large skillet or wok over medium heat. Add cubed chicken and cook, stirring occasionally, until golden on the outside and no longer pink inside, about 10 to 12 minutes.

Pour the sauce mixture over the chicken. Bring to a boil, then reduce heat to low, cover, and simmer for 30 minutes, stirring occasionally.

While the chicken simmers, bring 2 cups of water to a boil in a saucepan. Add rice, reduce heat to medium-low, cover, and simmer until rice is tender and liquid is absorbed, about 20 to 25 minutes.

In a small bowl, stir together cornstarch and cold water until smooth. Pour into the chicken mixture and stir to combine. Cook for a few minutes until the sauce thickens.

Serve chicken and sauce over rice. Garnish with chopped green onions.