Heat water in a saucepan, add onion and garlic, and stirring often for 5 minutes until onion is soft.
Add mushroom. Cook and stir for 2 minutes.
Add water, cornstarch (dissolved in water), and tamari. Stir continuously and simmer until thickened slightly, about 10 minutes.
Season with salt and pepper. Serve warm.

1-1/2 cup mushroom, chopped
1 medium onion, chopped
2 cloves garlic, minced
2-1/4 cup water
5 teaspoon cornstarch dissolved in 1/4 cup water
3 tablespoon tamari sauce
salt and pepper