Preheat the oven to 400 F. Use a damp paper towel to clean off any dirt on the mushrooms. Cut the mushrooms into one to two inch pieces, discarding the stems. Place mushrooms on a large baking sheet, sprinkle with salt and pepper, and toss with olive oil. Spread mushrooms into a single layer and bake for 25 minutes, or until golden brown.
For the gremolata
In a medium bowl, whisk together the 4 tbsp olive oil, lemon zest, kosher salt, capers, parsley, and minced garlic clove. Give it a taste for any salt. If it's dull, add a squeeze of lemon juice and mix again.
Slice the bread into ½ inch thick slices. Preheat a grill pan or skillet to medium high heat. Add a drizzle of olive oil. Grill each piece of bread until golden brown or until there are grill marks on one side, and flip. Cook the other side until golden. Remove to a plate.
To assemble, top each bread slice with mushrooms, then drizzle each with a spoonful of gremolata. Top with shaved parmigiano reggiano if using. Serve immediately.
Recipe by Tastemaker Blog at https://tastemakerblog.com/2020/11/11/maitake-mushroom-toast-with-gremolata/