Add the mushrooms and cook for another 3-5 minutes. If you're using vegan meat substitute, add it to the pan and cook until browned. Set aside the veggie-meat mixture.
After prepping your baking dish with parchment paper, place a layer of bread across the bottom until it's well covered, then place a layer of spinach leaves over the top.
Pour the rich filling over the crusty bread and fresh spinach, then smooth it out with a spoon or spatula. This ensures every bite is perfectly soaked and flavorful.