Preheat oven to 350°F (180°C). Grease a 9-inch quiche pan with olive oil.
In a skillet, sauté onion in olive oil until soft. Add ground beef and cook until browned. Drain all excess grease.
Add mushrooms to the skillet. Sauté until golden. Stir in garlic and Worcestershire sauce for 1 minute. Remove from heat.
In a separate bowl, whisk eggs, cream, salt, and pepper.
Place beef mixture in the pan. Top with shredded cheese and feta. Pour egg mixture over.
Bake for 35–45 minutes until set. Rest for 10 minutes before serving.
