In a small bowl, mix together the soy sauce, fish sauce, oyster sauce, and sugar. Set aside.
Heat the vegetable oil in a large wok or skillet over medium-high heat. Add the sliced beef and stir fry for 2-3 minutes until browned. Remove the beef and set aside.
In the same wok, add the minced garlic and stir fry for about 30 seconds until fragrant. Then add the sliced red bell pepper and green beans, cooking for another 2-3 minutes until they begin to soften.
Return the cooked beef to the wok. Pour in the prepared sauce and sprinkle with chili flakes. Stir everything together and cook for an additional 2 minutes until everything is heated through.
Remove the wok from heat, and stir in the fresh basil leaves until they are wilted and fragrant.
Serve the Thai Basil Beef Stir Fry hot over cooked jasmine rice.
Notes
Adjust chili flakes according to your heat preference.