Pre-heat oven to 425.
Butterfly chicken breasts and pound so that the chicken is about the same thickness throughout.
Saute onion and garlic in 2 T. butter. Off heat, mix in spinach, S&P, feta, oregano, lemon juice and a sprinkle of nutmeg (optional).
Stuff chicken with mixture, keeping closed with toothpicks. Place in oven safe dish.
In a bowl, melt 3 T. butter, add in breadcrumbs. Add this mixture to any remaining spinach mixture, and top the chicken before baking.
Bake 25-30 minutes.
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