How to Make It
Preheat oven to 400°F.
Combine spinach and onion in a microwave-safe bowl; cover and microwave at HIGH 1 to 2 minutes. Drain. Let stand in colander 5 minutes, pressing with the back of a spoon to release excess liquid.
Roll out puff pastry to a 14- x 12-inch rectangle on a large piece of parchment paper. Place parchment paper with puff pastry on a baking sheet. Score a 1-inch border around edge of puff pastry with a paring knife; prick area inside border several times with a fork. Bake for 14 minutes or until light golden. Remove from oven.
Combine spinach mixture, ricotta, garlic, salt, and feta in a bowl. Spread spinach mixture over puff pastry, inside border. Bake for 13 minutes or until crust is golden brown.
Combine pimientos, oregano, and vinegar in a bowl. Sprinkle pimiento mixture and pine nuts over tart. Cut into 12 slices.