Preheat oven to 400F. Spray 2 sheet pans with oil and set aside.
Gently remove the stems from the mushrooms and place stem-side down on the sheet pan.
Spray with olive oil and sprinkle with 2 pinches of salt and pepper, to taste.
Finely chop stems and place them in a large mixing bowl.
To the large bowl, add the spinach, cream cheese, ½ cup parmesan cheese, mozzarella, scallions, garlic, sour cream, ¼ teaspoon salt and pepper to taste. Mix with a fork to thoroughly combine.
Flip mushrooms stem-side up and stuff each mushroom with about 1 tablespoon filling, depending on the mushroom size, pressing mixture into the cavity of the mushroom and a small mound on top.
In a small bowl, combine the breadcrumbs and remaining 2 tablespoons parmesan cheese.
Top each stuffed mushroom with a sprinkle of breadcrumb mixture, gently spray tops with olive oil and bake for 25-30 minutes, rotating pans halfway through cooking to allow for even browning.
Allow to cool slightly and with a spatula, transfer to serving platter to serve warm or at room temperature.