Pour olive oil in pot over medium heat and add both types of onion. Saute for 1 minute, and then add spinach. Saute for approximately 10 minutes.
Preheat the broiler.
Pour spinach mixture in a bowl and cool. Add dill, eggs, feta and pepper to spinach mixture and mix very well.
Butterfly chicken breasts and fill with spinach/feta mixture. Close the breast and broil for 10 minutes on each side. After 15 minutes, douse chicken breasts with olive oil, lemon and oregano, and serve.
Recipe courtesy of The Parthenon