To make the cream of mushroom, heat a large skillet over medium-high heat and add 1 tbsp oil. Add the onions and saute for 3-5 minutes until onions are translucent.
Reduce the heat to medium and add the chopped mushrooms, salt, and saute for about 5-8 minutes until the mushrooms have cooked down completely. Add the garlic and cook for another minute.
Sprinkle the flour over the mushrooms and saute for about 1 minute until all of the mushrooms are covered with flour.
Using a whisk, whisk in the dairy-free milk until completely combined. Continue to whisk until the mixture has thickened, about 3-5 minutes.
Add the pepper, garlic, powder, and continue to cook for another 3-5 minutes. Taste and adjust seasonings as needed. Once the soup is thick, remove from the heat.