Steps:

Preheat oven to 200C (390F).
Heat olive oil in a pan, add onion and garlic, and cook until softened.
Add mushrooms, soy sauce, thyme, and rosemary. Cook until mushrooms are soft.
Stir in spinach until wilted, then remove from heat. Season with salt and pepper.
Mix ground flaxseed with water in a small bowl to create flax ‘eggs’. Let it thicken for a few minutes.
Roll out the puff pastry. Place the mushroom mixture in the middle, then fold over the pastry to encase the filling. Seal the edges.
Place on a baking sheet, brush with olive oil, and bake for 25-30 minutes, or until golden brown.
Allow to cool for a few minutes before slicing and serving.

Vegan Mushroom Wellington