Preheat the oven to 400°F. Lightly flour a clean work surface and roll 1 pastry sheet to 12 x 12-inch square. Slice into 4 squares (6-inches each). Repeat with the second sheet.
Beat 1 egg in a small bowl with 1 tablespoon water. Set aside.
Place the 2 eggs, onion, spinach and cheeses in the blender jar in the order listed and pulse until combined. Scrape down the sides of the jar and pulse again until almost smooth. Spread 2 tablespoons spinach mixture over each pastry square, leaving a 1-inch edge on all sides. Fold in half to form a triangle, then fold again to form a triangle. Brush the top and edges of the triangles with the egg/water mixture and pinch to lightly seal. Sprinkle with sesame or poppy seeds, if using.
Bake on a greased baking sheet for 20 minutes, or until golden brown. Serve with sweet chili sauce, if desired.