Heat 2 tablespoons olive oil in a large pot over medium heat until shimmering.
Add 1 medium onion, diced, and cook, stirring occasionally, until the onion is translucent, about 4–5 minutes.
Add 4 cloves garlic, minced, and cook, stirring, until fragrant, about 30–60 seconds (do not let the garlic brown).
Add 1 1/2 pounds fresh mushrooms, sliced, plus 1/2 teaspoon onion powder, 3/4 teaspoon dried basil, and 3/4 teaspoon dried oregano. Sauté, stirring occasionally, until the mushrooms soften and release their juices, about 5 minutes.
Pour in 4 cups vegetable broth and 1 can (14 ounces) full-fat coconut milk. Stir to combine.
Bring the soup to a gentle boil, then reduce the heat to low and simmer, uncovered, for 20 minutes, stirring occasionally.
Taste and season with kosher salt and black pepper to taste.
Ladle into bowls and garnish with chopped fresh parsley, if desired. Serve hot.