Thaw the fillo dough - according to the package - overnight in the fridge, or for about an hour or so on the counter.
Refer back to the earlier recipe for the pepper filling - if you start from scratch, that will work fine - just add the spinach. If you have extra left over from your earlier pepper appetizers - just add a bit more greek-style yogurt, a bit more feta cheese, and one 10-ounce package frozen chopped spinach - thawed and squeezed dry. Mix everything together in a bowl, and get ready to assemble.
On a cutting board, spray and layer three sheets of fillo dough - placing one sheet, lightly spraying with cooking spray (also known as "Pam"), next layer - lightly spray, last layer - lightly spray. Cut the layered fillo in half lengthwise.
Place one tablespoon of the filling about 1 inch from the corner of each strip. Fold one corner of the fillo diagonally across to the opposite edge to form a triangle.
Spray lightly with Pam and continue to fold the triangle onto itself - until it's all folded up into a cute little triangle. (I don't know why this is underlined?)
My "fillo" box recipe said to spray the outside of the triangle - but I found that with all the Pam spraying already going on, there was plenty of Pam spray to produce the desired result (a golden brown color when baked).
Place triangles, seam side down on ungrease cookie sheet at least 1 inch apart. Bake in preheated oven (350 degrees) for 20 - 25 minutes - until golden brown.
We enjoyed these at the "OUTFEAST" sing-a-long showing of "Best Little Whorehouse In Texas" at the beautiful outdoor Ford Amphitheatre - with special guest, Megan!