In a small bowl, combine the oyster sauce, low-sodium soy sauce, fish sauce, and sugar. Mix thoroughly until the sugar is dissolved. If the sauce is too thick, add a splash of water to reach your desired consistency. Set it aside.
In a wok or large skillet, heat the peanut or coconut oil over medium-high heat. Make sure the oil is hot before adding the chicken to ensure it sears properly.
Add the bite-sized pieces of chicken thighs to the hot oil. Cook for about 5-7 minutes, stirring frequently until the chicken is browned and cooked through. Remove the chicken from the pan and set it aside.
In the same pan, add minced garlic and Thai bird chiles. Stir-fry for about 30 seconds, or until fragrant. Be careful not to let the garlic burn.
Next, add the chopped scallion whites, red bell pepper, and green beans to the pan. Stir-fry for about 3-4 minutes until the vegetables are tender-crisp.
Return the cooked chicken to the pan. Pour the prepared sauce over the chicken and vegetables. Toss everything together to coat evenly in the sauce. Cook for an additional 2-3 minutes, allowing the sauce to thicken slightly.
Just before serving, add the fresh Thai basil leaves. Toss them in briefly until just wilted. The residual heat will release the basil's aromatic oils.
Serve your Thai Basil Chicken hot over steamed rice or noodles. Garnish with the green parts of the scallions for an extra pop of color. Enjoy the delightful flavors of your homemade Thai dish!