Heat (14-inch) skillet over medium-high heat, and then add oil and onion,
Sauté to soften onion slightly, about 2 minutes. Stir tomato, ginger, if using, and red pepper flakes. Cook for an additional 2 minutes. Add cabbage and salt. Stir to combine.
Cover, reduce heat to medium low and cook, stirring occasionally, as the cabbage begins to collapse.
Add a little water (2 Tbsp.) at a time, as needed if the cabbage becomes too dry.
Cook for about 13 minutes or until the cabbage is just tender. Season with salt to taste and serve.