Preheat the oven to 400 degrees F. Line a large cookie sheet with parchment paper; set aside.
To cook the spinach, heat the olive oil in a large sauté pan over medium heat. Add the onion and spinach and cook 1 to 2 minutes, or until spinach is wilted. Remove from heat.
Unfold the puff pastry onto a sheet of parchment paper. Cut each puff pastry sheet into 4 squares and place on the prepared cookie sheet. Divide the cooked spinach among the squares. Top each pastry with a piece of cheese and one tablespoon of cranberry sauce, reserving as much of the liquid as possible from the sauce. Fold each square in half diagonally and press edges together with a fork to seal.
Whisk together the egg and water, then brush the tops of each turnover. Bake for 15 to 17 minutes until the pastry is golden brown and cooked through. Remove from the oven and let cool.