Preheat oven to 375. Carmelize onions on high heat until golden. Add 1 cup water, mushrooms, bacon, garlic to onions and cook until all water is reduced. Set aside to cool.
In separate bowl, beat eggs then add heavy cream, cheese and onion/mushroom mixture. Gently fold in spinach and pour mixture into the pie crusts. Bake for 40-45 minutes until lightly golden on top and egg mixture has set.
This makes enough filling for 3 shallow pie crusts.