Gluten Free Vegan Stuffed Mushrooms Recipe

I'm having guests again this week (its not something we end up doing so often, but lately I guess we're having guests more than usual) and wanted to do something nice for them. I know that lots of the food that I cook is relatively exotic, and not everyone enjoys exotic foods as much as I do, so I make sure to ask my guests if they'd prefer more exotic or more "normal" foods when they come over.
I know some people have the mindset that if someone comes to someone else's house as a guest, they should just appreciate whatever is given to them, and there is no need to go out of your way as a host to make foods that your guests will like- that people should just eat what is served to them. And while that may be true as part of being a gracious guest, as a hostess, I believe my part is to make my guests as comfortable as possible, and give them the best that I physically/financially/emotionally can afford to do so. (I wrote about it, actually, in my post about Extreme Cheapskates, and specifically how about the person who fed salmon carcasses and salmon heads to the people who he cooked dinner for- and made them feel like puking.)
So anyhow, these guests chose "normal" food, but that doesn't mean I want to make it boring and simple. My challenge was to come up with something nice and impressive and tasty, that still fell under the realm of "normal" and "non exotic". While grocery shopping, I saw these large fresh white button mushrooms, each with a 3-4 inch diameter, and inspiration struck- stuffed mushrooms it would be. And vegan, to keep it cheaper, (Don't worry- I'm serving other dishes as well, this is just one of the things I'm serving...)
They came out great, and I look forward to serving them to my guests.

Gluten Free Vegan Stuffed Mushrooms Recipe

Ingredients:
9 extra large mushrooms- or more smaller
1 cup finely minced onion (this was about half of an extra large onion)
1 cup finely minced mushroom stems (this was the stem from my 9 xl mushrooms)
1 cup cooked brown rice (leftover rice is fine- and feel free to use any other cooked grain, like white rice or quinoa)
2 cloves fresh garlic
1 tablespoon finely chopped rosemary (I used foraged rosemary)
1/2 cup white wine or broth (I used wine that I bought at the scratch and dent store, but homemade broth is fine)
1/4 cup finely chopped celery (including the leaves)
3/4-1 1/2 teaspoon salt (1 1/2 tsp salt will result with these being on the saltier side, so use less if you don't like things salty)
1 teaspoon powdered sage
1 tablespoon olive oil or other oil of choice, plus more oil for drizzling
1/2 cup roughly chopped walnuts (any nuts or sunflower seeds would work as well- and it would probably work fine without the walnuts- just add an extra 1/2 cup brown rice in its stead)
1/4 teaspoon ground black pepper (optional)

Instructions:
1. Remove the stems from your mushrooms, and lay your mushrooms tops out on a tray.

2. Chop up all the other ingredients very small, minus the walnuts, and mix them all together- excluding the walnuts.

3. Take half of the mixture, and put it in a food processor for about 20 seconds. You don't want it smooth, just not as chunky as it was before.

4. Mix the processed mixture with the unprocessed mixture,

5. Roughly chop your walnuts, and mix them in.

6. Fill your mushroom caps, pressing in the mixture and making it into a mound over the top. This mixture should be the perfect amount for the mushrooms.

7. Drizzle a little oil on the baking tray. Cover it loosely.

8. Bake at 350 for 30 minutes, then remove the cover and bake for 20 more minutes.

9. Serve warm.

Enjoy!

Have you ever made stuffed mushrooms? What do you put in them? Does this look like a recipe you'd try?
What is your "go to" cheaper and "non exotic" meal that you'd make when you're trying to make something impressive for guests or otherwise?