Finely chop 1 ½ lbs of mushrooms and set aside. Heat 1-2 tablespoons of olive oil in a skillet over medium heat. Sauté 1 large chopped onion until translucent, about 3 minutes.

Add the chopped mushrooms and season with salt, pepper, and 4 twigs of thyme, frying for an additional 5 minutes until mushrooms are golden. Drain any excess moisture.

In the same skillet, briefly sauté 4 minced garlic cloves for 30 seconds until fragrant. Add ⅔ cup of baby spinach and stir until wilted.

In a large bowl, mix the cooked mushrooms and onions, sautéed spinach, ⅔ cup of cooked rice, and optional ¾ cup of chopped walnuts or pecans.

Stir in 2 tablespoons of mustard, the optional ½ cup of vegan cheese, and add 2-3 tablespoons of fine oats if desired. Adjust the seasoning.

Tightly wrap the filling mixture in aluminum foil and refrigerate for about 30 minutes.

Preheat your oven to 390°F (200°C) and roll out a sheet of vegan puff pastry. Place the cooled filling mixture along the center and fold the sides over to enclose.

Brush the top with 2-3 tablespoons of plant-based milk mixed with a pinch of turmeric. Bake for 20-25 minutes until golden and flaky.