Preheat the oven to 400 degrees.
To clean the mushrooms, remove the stems and use a spoon to scoop out the dark gills inside.
Brush both sides of the mushrooms with olive oil. Place them on a baking sheet with the cap facing down. Bake for 10 minutes.
While the mushrooms bake, cook the ground beef in a pan over medium heat until it's no longer pink. Drain the extra fat.
Add feta cheese, sun-dried tomatoes, kalamata olives, parsley, dill, oregano, garlic, and tomato sauce to the cooked beef. Mix everything well. Add salt and pepper to taste.
Spoon the meat mixture into the baked mushrooms and bake for 15 minutes.
Sprinkle fresh parsley on top and enjoy!