Heat a large non-stick, cast iron pan, or wok over medium high heat. Add the oil.
When hot, sauté the onions, ginger, and garlic until tender and aromatic, around 1 minute.
Over high heat, add in the broccoli florets. Pour ¼ cup vegetable broth and then cover the pan. Leave the broccoli to cook over medium high heat until half-cooked or cooked and crisp to your liking. Move to the side of the pan.
Add some more oil. Add in the bell peppers and sauté for a few minutes until tender. Move to the side of the pan.
Add in the mushrooms or plant-based protein of choice. Season the mushrooms/protein with dark soy sauce, if desired for color. Allow the mushrooms/plant-based protein to get a nice sear or light brown before mixing everything together.
For the sauce: be sure to give the sauce a good mix again to ensure the cornstarch doesn't stick to the bottom. Pour in the sauce mixture.
Lower the heat. Mix everything together and leave to simmer over medium heat until the sauce has thickened from the cornstarch.
Taste the broccoli and feel free to season with more soy sauce or vegetarian oyster sauce, if needed. Turn off the heat.