Heat 2 tablespoons of olive oil in a skillet over medium heat. Add the finely chopped onion and minced garlic, and sauté for about 3-4 minutes until the onion becomes translucent and fragrant.

In a large mixing bowl, combine the sautéed onion and garlic with 2 cups of chopped fresh spinach, 1 cup of crumbled feta cheese, and 2 beaten room temperature eggs. Mix until creamy.

Preheat your oven to 375°F (190°C). Line a square baking dish with parchment paper or lightly grease it with olive oil.

On a floured surface, roll out the thawed puff pastry into a large square about 1/8 inch thick. Fit it into the prepared dish.

Spread the spinach and feta mixture evenly over the puff pastry in the baking dish.

Place the filled baking dish in the preheated oven and bake for approximately 25-30 minutes until golden brown.

Remove from the oven and allow to cool for about 5 minutes before slicing.