Preheat your oven to 375°F (190°C).

Rinse the spinach thoroughly and chop it coarsely.

In a large skillet, heat 2 tablespoons of olive oil over medium heat and sauté the chopped onion until translucent, about 5 minutes.

Add the chopped spinach to the skillet, and cook until wilted, about 5-7 minutes. Remove from heat and let it cool slightly.

In a bowl, combine the cooled spinach mixture with crumbled feta, dill, salt, pepper, and the beaten egg. Mix well until combined.

Unroll the phyllo pastry and cover it with a damp towel to prevent it from drying out. Take one sheet of phyllo, brush it lightly with olive oil, and fold it in half lengthwise.

Place a tablespoon of the filling at one end of the folded phyllo, and fold over to form a triangle. Continue folding, keeping the triangle shape until you reach the end of the pastry.

Repeat the process with the remaining phyllo sheets and filling. Arrange the triangles on a baking sheet lined with parchment paper.

Brush the tops of the triangles with remaining olive oil before placing them in the oven.

Bake the triangles in the preheated oven for 25-30 minutes or until golden brown and crisp.

Remove from the oven and allow to cool slightly before serving.