Combine rice vinegar, granulated sugar, and oyster mushroom sauce in a small bowl.

On high heat, add water and salt in a pot and bring the mixture to a rolling boil.

Stir in the spinach and blanch for 30 seconds.

Strain and place on an ice bath until it cools down.

Roughly chop the blanched spinach and place it in a serving bowl.

Add in onion slices, tomatoes, and bell peppers.

Pour the dressing over and mix well and serve immediately.

Enjoy a delicious spinach salad!