Cook the wild rice according to package instructions.
In a large skillet, heat the olive oil over medium heat. Add the onions, celery, and mushrooms. Cook until softened.
In a large mixing bowl, combine the cooked wild rice, sautéed vegetables, chicken broth, and half of the shredded cheese. Season with salt and pepper to taste.
Transfer the mixture to a baking dish. Top with the remaining cheese.
Bake in the preheated oven for 30 minutes, or until the cheese is melted and bubbly.
Notes:
This casserole can be made ahead and refrigerated. Just bake it when you're ready to serve.