Preheat your oven to 375°F (190°C).
Gently remove the stems from the mushrooms and set the caps aside. If the mushrooms have a lot of moisture, pat them dry with a paper towel.
In a small bowl, combine the crumbled feta cheese, chopped sun-dried tomatoes, garlic powder, oregano, and black pepper. Mix well.
Drizzle the mushroom caps with a little olive oil, and then stuff each mushroom cap with the feta and sun-dried tomato mixture.
Place the stuffed mushrooms on a baking sheet lined with parchment paper or foil.
Drizzle with a little more olive oil and bake in the preheated oven for 15-20 minutes, or until the mushrooms are tender and the cheese has softened.
Garnish with freshly chopped parsley before serving.