In a bowl, stir together warm water, brown sugar, orange juice, tamari, ketchup, white vinegar, garlic, red pepper flakes, five-spice powder, and orange peel until the sugar has dissolved and mixture is well combined.
Heat olive oil in large skillet/wok over medium heat. Cook and stir chicken until outside is golden brown and inside is no longer pink; about 10 minutes.
Pour sauce mixture over the chicken, bring to a boil, and reduce heat to medium-low; cover skillet. Simmer for 30 minutes, stirring occasionally.
Whisk cornstarch and 2 Tbsp cold water in a small bowl until smooth. Then, stir into sauce slowly, a few tsp at a time. Let chicken and sauce cook for about 2 minutes to thicken. Serve with a side of rice or quinoa (pictured above). Sprinkle green onion over top, if desired.
Notes
Recipe adapted from "Mama's Asian Chicken and Rice" recipe by Scarlett; found at www.allrecipes.com.