Preheat your oven to 425°F (220°C). In a large mixing bowl, combine well-drained and chopped spinach, chopped artichokes, grated Parmesan, Gruyère, cheddar, minced garlic, lemon zest, red pepper flakes, and salt.

On a lightly floured surface, roll out a sheet of puff pastry to a 10"x10" square, and slice into rectangles, about 4"x6".

Take one rectangle of puff pastry, add a spoonful of the filling along one edge, brush the opposite edge and sides with a beaten egg, roll gently and seal with a fork.

Place the rolls on a baking sheet lined with parchment paper, cover with plastic wrap, and chill in the freezer for about 20 minutes.

Slice each log into bite-sized pieces, arrange on a baking sheet, brush with egg wash, and bake for 25 minutes until golden brown.

Let the rolls cool slightly on the baking sheet for five minutes, then transfer to a serving platter and serve warm.