In a small bowl, whisk together the oyster sauce, light soy sauce, dark soy sauce, fish sauce, and brown sugar until the sugar is fully dissolved. Set this stir-fry sauce aside.

Heat 1 tablespoon of vegetable oil in a large wok or skillet over medium-high heat until shimmering. Add the thinly sliced beef in a single layer and let it sear undisturbed for 1 to 2 minutes to develop a brown crust.

Stir the beef and continue cooking for another 2 minutes until just browned on all sides, then remove the beef from the wok and set aside on a plate.

In the same wok, add the remaining 1 tablespoon of oil. Toss in the minced garlic and sliced chilies, stirring constantly for about 30 seconds until highly fragrant.

Add the sliced red bell pepper to the wok and stir-fry for 2 minutes until it begins to soften but still retains a slight crunch.

Return the beef and any resting juices to the wok, pouring the prepared sauce over the top. Toss everything together for 1 to 2 minutes until the sauce bubbles and beautifully coats the beef.

Remove the wok from the heat and immediately stir in the fresh Thai basil leaves. Toss gently until the basil is just wilted and fragrant, about 30 seconds.

Serve immediately over a bed of hot steamed jasmine rice. Top with a crispy, sunny-side-up fried egg for a truly authentic Thai homestyle experience.