Heat oil in a medium saucepan.
Add onion, garlic, mushrooms, thyme and tamari/coconut aminos.
Simmer on medium-low heat until the mushrooms are tender and the onions become transparent. (If you would like whole mushroom and onion chunks in your gravy, remove half from the saucepan and place in a bowl at this point).
Add vegetable broth, water and arrowroot flour.
Bring to a low boil over medium-high (Too high of a heat will make the arrowroot lose its thickening ability).
Once it begins to bubble, turn the heat down to low and let simmer for about 5 minutes, stirring intermittently.
Remove from heat and let cool.
Once cool, add salt and blend until smooth.
If whole mushrooms were removed, stir them back in.