Add olive oil to a large pot on medium-high heat.Add onions and sauté until translucent (about 5 mins).Add celery and cook for another minute before adding mushrooms.Let mushrooms cook for about 10 mins or until they've reduced in size. They will appear as if they are "sweating".Add vegetable broth, wild rice, thyme, sea salt and pepper and bring to a boil.Lower heat to a simmer and cover. Let simmer for 30 minutes or until rice is fully cooked (time will depend on the type of wild rice you use so you may need a bit longer than this.Remove top and simmer for another 10 minutes.Serve warm.