vegetable oil
onion, finely chopped
Kosher salt
cloves garlic, minced
cream cheese, softened
eggs, divided
(10-oz.) package frozen spinach, thawed and squeezed as dry as possible
crumbled feta
fresh dill, chopped
lemon zest
Freshly ground black pepper
Cooking spray
All-purpose flour, for rolling puff pastry
sheet from 1 (17.3-oz) package puff pastry, thawed in the refrigerator