Gather all ingredients.
Whisk together oyster sauce, fish sauce, and sugar in a small bowl; set aside.
Heat oil in a wok over medium-high heat until oil begins to smoke. Add garlic and Serrano peppers, stirring quickly.
Stir in chicken, bell pepper, onion, and oyster sauce mixture; cook until chicken is no longer pink in the center and the juices run clear.
Increase heat to high and stir in chilled rice; stir quickly until sauce is well blended with rice. Use the back of a spoon to break up any rice sticking together.
Remove the wok from heat. Stir in basil leaves. Garnish with sliced cucumber and cilantro.
