Position rack in center of the oven and preheat the oven to 350 degrees F. Line a large baking sheet with parchment paper.
Place the spinach in a wire-mesh strainer or colander, place over a sink and drain well. Use your hands or a paper towel to squeeze the excess water out of the spinach.
Place the spinach in a medium mixing bowl. Add the salt, pepper, oregano, parsley, and basil. Stir in the beaten egg, olive oil, and lemon juice. Add the feta cheese and mix well to combine. Set aside.
Gently unfold the phyllo dough.* Lay 1 sheet of phyllo on a large cutting board and gently brush with the melted butter. Place a second phyllo sheet on top of the first and brush with butter. Repeat 2 more times until you have a stack of 4 phyllo sheets with butter brushed between the layers.
Using a sharp knife, cut the phyllo sheets lengthwise into 3 strips. Place 2 tablespoons of the spinach filling 1 inch from the bottom end of each strip.
Take the bottom right corner of the strip between your thumb and finger and fold over the spinach filling to the left to make a triangle. Gently pull up the bottom left corner and fold up to make a second triangle. Continue folding until you reach the top. Place the triangle, seam side down, on the prepared baking sheet. Brush the completed triangle lightly with butter.
Repeat with the remaining strips and phyllo sheets until all of the filling is used.
Arrange the triangles 2 inches apart on the baking sheet. Bake for 15 minutes, until golden and heated all the way through. Remove the spanakopita from the oven and cool slightly on the baking sheet.
Serve warm or at room temperature.
*It is important to keep a piece of plastic wrap and a damp cloth or paper towel over the phyllo sheets that you are not working with to keep them from drying out.