Use your hands to gently separate the cold grains of rice (this will make them easier to add to the pan). Set aside.
Whisk together oyster sauce, soy sauce, rice vinegar, fish sauce, sugar, and cooking oil and set aside.
Heat oil in a wok or a nonstick skillet over medium heat. Add the onions and saute until the onions are soft, 3 to 4 minutes. Add the garlic and chilis and saute until fragrant, about 1 minute more.
Pour the sauce over the onions. When the sauce is bubbling, add the rice and stir everything together until combined.
Spread the rice out in a single layer. Let the rice cook, without stirring, until it is crisp and golden where it meets the pan, 4 to 5 minutes. (Remove a portion of the rice to check for crispness on the bottom.)
When the rice is crisp, stir in the basil leaves and cashews. Keep stirring until everything is heated through and the basil is wilted.
Serve warm with fried eggs on top if you’d like.
