Heat the oil in a small pot over medium heat. Add the flour and continuously whisk for 2 to 3 minutes. Slowly add in the broth and whisk until smooth.  Add nutritional yeast, tamari, onion and garlic powders. Continue to cook, whisking continuously, until the mixture is thick and velvety. Taste and add salt if necessary. Thin to desired consistency with more broth. Store extra in a covered container for up to 5 days or freeze for up to 3 months. Gravy will thicken considerably when chilled. Microwave or heat on the stove top, adding more broth to thin if necessary.