Cook the rice: In a medium saucepan, cook the brown rice according to package instructions. Once cooked, set aside to cool.

Preheat the oven: Preheat your oven to 350°F (175°C) and grease a loaf pan or line it with parchment paper.

Cook the vegetables: In a spacious skillet, warm the olive oil over medium heat. Stir in the diced onion, minced garlic, and chopped celery, cooking them for 5 to 7 minutes until they become tender and aromatic. Season with salt and pepper to taste.

Cook the mushrooms and spinach: Add the sliced mushrooms to the skillet and cook for another 5 minutes until they release their moisture and become tender. Add the fresh spinach and sauté for another 2 to 3 minutes until it has wilted. Take the pan off the heat and let the mixture cool for a few moments.

Combine the ingredients: In a large mixing bowl, combine the cooked brown rice, the sautéed vegetable mixture, sun-dried tomatoes, and chopped tarragon. Stir in the whisked eggs, Dijon mustard, and vegetable broth until everything is well combined.

Transfer to loaf pan: Pour the mixture into the prepared loaf pan and smooth the top with a spatula.

Bake the loaf: Bake for 35-40 minutes, or until the loaf is set and a toothpick inserted into the center comes out clean.

Cool and serve: Allow the loaf to cool for a few minutes before slicing. Enjoy it warm alongside your preferred side dishes or a refreshing salad.