Preheat the oven to 375°F. Grease a medium-sized loaf pan or ring mold. You can also use parchment paper to prevent from sticking.
Finely chop the mushrooms, celery stalks, and onion. Process them separately in a food processor or just use a knife, making sure they’re chopped in small, fine pieces. Use a cheese grater to finely grate the carrot as well.
Add all the chopped and grated veggies to a large pan on medium heat. Oil is optional but can be used to prevent sticking to the pan. Add the rest of the “wet ingredients,” including the rice, soy sauce, and spices, then stir to combine with the chopped veggies. Saute for 10 minutes. Taste a small amount of the mixture here and adjust the seasoning as needed.
Using a food processor again, pulse the cup of mixed nuts into a coarse flour but do not fully grind them up. Then combine all the dry ingredients including the nuts into a large mixing bowl. Mix in the sauted “wet ingredients” to the bowl, thoroughly combining with the dry, until a dough-like texture forms.
Taking a small amount at a time, add the mixture to the loaf pan or ring mold and lightly press down each layer with a spatula. Here, you can also lightly press in extra thyme or mushrooms on top for decoration.
Bake the loaf in the oven for 1 hour. Do the toothpick test to make sure it has cooked through, then remove from the oven and let cool for at least 15 minutes before carefully removing it from the pan or slicing.
Enjoy as a main dish with mashed potatoes and gravy!