In a large Dutch oven over medium-high heat, add the avocado oil. Cook the mushrooms in batches until they are golden brown. Add the onion and celery and let cook for 5 minutes.

Add the chicken stock, wild rice, parsley, onion and garlic powder, and mushroom powder, if using. Let simmer for 45 minutes over low to medium-low heat until the wild rice has 'popped' as is tender.

While the soup is cooking, heat the butter in a small non-stick saucepan on the stove over low heat. Whisk in the flour and let cook until lightly golden brown.

Add to the simmering soup and stir until the soup has thickened. If you would like it thinner, add some additional stock to the pot.

Stir in the heavy cream right before serving.