Mince the garlic cloves finely and slice the bird's eye chilies into thin rounds, removing seeds if you prefer less heat. Chop the green onions, separating the white parts from the green parts and keeping them in separate piles. Roughly chop the Thai basil leaves and set aside. In a small bowl, combine the oyster sauce, soy sauce, dark soy sauce, fish sauce, sugar, and water, stirring until the sugar dissolves completely. This sauce base is crucial for building authentic Thai flavors, so take a moment to ensure it's well mixed.

Heat the 1 1/2 tablespoons of oil and sesame oil in a large skillet or wok over high heat until it shimmers and is just starting to smoke. Add the minced garlic and sliced chilies, stirring constantly for about 10 seconds—you want to bloom these aromatics and release their fragrance without letting them burn. Immediately add the white parts of the green onions along with the bite-sized chicken pieces, stirring and cooking for 2 minutes until the chicken is mostly cooked through. I like to keep the heat high here to get a slight caramelization on the chicken, which adds depth to the dish.

Pour the sauce mixture from Step 1 into the pan with the cooked chicken and aromatics, stirring constantly for about 1 minute to allow the sauce to coat everything evenly and reduce slightly. The sauce will cling to the chicken and create a glossy coating. Add the green parts of the green onions and the chopped Thai basil, tossing everything together for 30 seconds to 1 minute until the basil just begins to wilt but still maintains its vibrant color and fresh aromatics. Don't let the basil cook too long—you want to preserve its delicate Thai basil flavor, which is the signature of this dish.

Transfer the Thai basil chicken to a serving plate and serve immediately over steamed jasmine rice. The rice will absorb the flavorful sauce beautifully, bringing everything together.