Clean the oyster mushrooms and tear them into bite-sized pieces.
Slice the onion and green onion thinly.
Heat cooking oil in a pan and sauté the onion and green onion.
Add the oyster mushrooms and stir-fry together.
Add soy sauce, sugar, minced garlic, pepper, and water. Bring to a simmer.
Simmer over medium heat until the mushrooms absorb the seasoning.
Finish by drizzling sesame oil and sprinkling sesame seeds on top.