Vegan Shredded Mushroom Tostadas

1. Preheat oven to 400 degrees. Cut off woody base of mushrooms. Cut caps from stems and dice. Using a fork, shred base of mushroom, making long, deep cuts lengthwise from top to bottom around entire mushroom. Continue shredding until it comes apart easily. Repeat until all mushrooms are shredded.
2. In a wide pot or skillet over medium-high heat, warm 1 tablespoon of oil, add half of mushrooms in an even layer, and cook for 8 to 12 minutes until well-browned. Add ⅛ teaspoon of salt and ⅛ teaspoon of pepper and transfer to a bowl. If skillet seems dry, add another drizzle of oil. Once warmed, add remaining mushrooms and cook for 8 to 12 minutes. Season with remaining ⅛ teaspoon of salt and ⅛ teaspoon of pepper.
3. Return all mushrooms to pot and season with 2 teaspoons Mexican spice blend. Toss to coat. Add half scallions and pour in ½ cup water or stock. Bring to a boil, then reduce heat to low and simmer for 10 minutes.
4. In a pot over medium heat, warm remaining 1 tablespoon oil. Once hot, add remaining scallions and cook for 1 minute. Add remaining Mexican spice blend, toss to coat, and cook for 1 minute more. Add beans and remaining water or stock. Bring to a boil, then reduce heat to medium and rapidly simmer for 10 minutes or until liquid reduces. Turn off heat. Use an immersion blender or potato masher to blend beans until smooth. 
5. Brush a baking sheet with a teaspoon of neutral oil. Brush 4 tortillas with a drizzle of oil. Place on top of baking sheet and place in oven for 5 minutes. Flip and return to oven for another 5 to 10 minutes until browned and crispy. Remove baking sheet from oven and bake remaining tortillas until crisp.
6. Onto each tostada shell, spoon beans and pile a scoop of shredded mushrooms on top. Garnish with lettuce, cilantro, radishes, and pickled red onions.