Rinse rice under cold water until it runs clear, then add to a pot with double the amount of water and a pinch of salt. Bring to boil, cover, reduce heat, and simmer for about 15 minutes.

Heat olive oil in a skillet or wok over medium-high heat until shimmering.

Add the diced chicken, season with salt and pepper, and sauté for 5 to 7 minutes until golden brown and cooked through. Remove and set aside.

In the same skillet, add sesame oil, chopped onions, and minced garlic. Sauté for about 2 minutes until onions are translucent.

Add broccoli florets and sliced mushrooms. Sauté for 4-5 minutes until tender-crisp.

Return cooked chicken to the pan, stir everything, then add soy sauce and oyster sauce (if using). Stir for another 2 minutes.

Mix cornstarch with water to form a slurry, then pour into the skillet while stirring. Allow sauce to thicken for 1-2 minutes.

Serve over rice, garnishing with sesame seeds or fresh cilantro if desired.