Preheat your oven to 375°F (190°C). Line a large baking sheet with parchment paper.

In a large skillet over medium heat, lightly sauté the diced onion until translucent. Add the chopped spinach and cook until wilted. Remove from heat and firmly squeeze out all excess moisture.

Transfer the drained spinach and onion mixture to a large bowl. Stir in the crumbled feta cheese, beaten eggs, parsley, dill, and lemon juice until thoroughly combined.

Unroll the phyllo dough on a clean, dry surface. Keep it covered with a damp kitchen towel to prevent it from drying out.

Place one sheet of phyllo on your work surface and lightly brush it with melted butter. Cut the sheet lengthwise into 3-inch wide strips.

Place a heaping tablespoon of the spinach and feta filling at the bottom end of one strip.

Fold one bottom corner of the phyllo over the filling to meet the opposite edge, forming a triangle. Continue folding the triangle onto itself, flag-style, until you reach the end of the strip.

Place the folded triangle onto the prepared baking sheet, seam side down. Repeat with the remaining filling and phyllo strips.

Brush the tops of all the triangles with the remaining melted butter.

Bake for 20 to 25 minutes, or until the pastry is puffed, golden brown, and crispy. Serve warm with a side of lemon yogurt dip.