1. Preheat the oven to 180°C (350°F). Clean the mushrooms and remove the stems. Place the caps on a baking sheet. Drizzle with a little olive oil, season with salt and pepper. Bake for 20 minutes, then let cool.
2. Rinse the quinoa several times with cold water. Cook it according to the package instructions. Drain it, put it in a salad bowl, and let it cool. Cook the bulgur for 5 minutes in salted boiling water. Drain and let it cool.
3. Peel and slice the onions. Wash the bell pepper, remove the seeds and white parts, then cut it into small cubes. Open the pomegranate and collect the seeds over a sieve placed in a bowl, reserve the juice. Crumble the mozzarella with a fork. Wash, dry, and separate the mint leaves. Chop them roughly.
4. Mix the whole grain mustard, vinegar, and olive oil. Add the pomegranate juice. Season with salt and pepper.
5. In the salad bowl, mix the quinoa, bulgur, bell pepper, onions, pomegranate, mint, and mozzarella. Drizzle with the sauce and mix well.
6. Divide the salad into the mushroom caps, add the crushed pistachios, and keep refrigerated until ready to serve.