Start by mixing your sauce ingredients. In a medium-sized bowl, combine the fresh orange juice, grated zest, soy sauce, rice vinegar, brown sugar, sriracha, and garlic. Stir well to ensure everything blends smoothly. Set this mixture aside—it’ll be added to the pan after the chicken is cooked.
Heat the vegetable oil in a large skillet over medium-high heat. Once the oil shimmers, add the bite-sized chicken pieces. Let them cook for 3 to 5 minutes, turning occasionally until they are golden brown on all sides. Season them lightly with salt and pepper during this step.
Pour the prepared orange sauce into the skillet with the browned chicken. Bring it to a light simmer, then reduce the heat to low. Let it cook gently for another 5 minutes so the chicken absorbs the citrusy-spicy flavors and becomes fully cooked through.
In a small bowl, mix the cornstarch with 1/4 cup water until smooth. Slowly stir this slurry into the simmering sauce. Within 2 to 3 minutes, the mixture will start to thicken into a glossy glaze that perfectly coats the chicken. Taste and adjust seasoning if needed.z
Serve the spicy orange chicken hot over a bed of steamed rice. Top with chopped green onions and fresh cilantro for added freshness and visual appeal. If you're planning a casual dinner, let guests garnish their bowls individually.