Wash the mushrooms and pat dry. Slice the mushrooms to resemble shredded meat. Add the spices to a mortar and grind the garlic cloves into the spices until it resembles a paste.
Meanwhile, heat olive oil in a saucepan and add the mushrooms. Add the spice paste and the vinegar. Cook over medium heat until the mushrooms are tender. Simmer for 15 minutes to allow spices to blend well. Mix arrowroot powder and water until dissolved. Add to the mushroom mix and bring to a boil. Cook for 5 minutes or until sauce thickens. Remove from heat.
For the Pickled Onions
Place onions in a medium pot and add water, vinegar, and spices. Bring to a boil and cook for 10 minutes. Remove from heat and cool. In order to get a good flavor, make the night before to ensure spices have come together.
Refrigerate onions and remove from the fridge while preparing the mushroom mix.
Remove bay leaves and peppercorns before serving pickled onions.
For the Black Bean Spread
Heat olive oil in a pan and fry the onions for 5-7 minutes until translucent.
Add the garlic and the beans with reserved liquid.
Add the oregano and bring to a low boil for 10 minutes.
Place beans in a deep bowl and using an immersion blender, blend the beans until smooth. You can also place in a blender and blend until smooth.
Preheat oven to broil. Line a baking sheet with parchment paper.
Cut each roll in half. Layer each half with 2-3 Tablespoons of black bean spread. For each sandwich: On 1 half of bread, add ½ cup of the mushroom mix and on the other half add ¼ cup Daiya mozzarella crumbles. Repeat with the rest of the rolls.
Place the 8 halves on a cookie sheet and broil until cheese melts and bread is somewhat toasted. Watch carefully.
Remove from oven and on each mushroom half, add 2 Tablespoons of pickled onions. Place the cheesy bean half of the bread on top. Serve warm.
Note: Nutrition information does not include buns.