Make the sauce by combining the soy sauce, oyster sauce, rice vinegar, sugar, and sesame seeds until the sugar is completely dissolved.
Heat the sesame seed oil in a large skillet or wok over medium-high heat. Saute the garlic slices until slightly brown. Add the red onion slices and trimmed green beans and cook until the green beans are almost done.
Once the green beans are almost done to your liking, pour in the sauce and simmer until the green beans are cooked to your liking.