Preheat the oven to 375°F (190°C) and line a large baking sheet with parchment paper.
Clean the mushrooms with a damp paper towel and carefully remove the stems to create a cavity for the filling.
In a medium mixing bowl, stir together the Greek yogurt, blended cottage cheese, chopped spinach, parmesan cheese, minced garlic, onion powder, and oregano.
Season the filling mixture with salt and pepper, adjusting to taste preferences.
Arrange the mushroom caps on the prepared baking sheet with the cavity side facing up.
Distribute the spinach protein mixture evenly among the mushroom caps, approximately 1 tablespoon per mushroom.
Top each stuffed mushroom with a small pinch of the shredded mozzarella cheese.
Bake for 18 to 20 minutes or until the mushrooms are tender and the cheese topping is golden and bubbly.
Remove from the oven and allow to rest for 3 minutes before serving.