A recipe for simple spanikopita triangles includes phyllo, feta cheese and frozen spinach. The recipe has a prep time of about 20 minutes, excluding the time required to cool the onion-spinach mixture.
Heat 1 tablespoon of oil in a large skillet set over medium-high heat. Add 2 cups of finely chopped onions to the skillet, and sauté until the onions are beginning to brown, about five to seven minutes. Add 2 10-ounce packages of frozen spinach, thawed, squeezed dry and chopped. Cook the spinach and the onions until the mixture is mostly dry, about three minutes. Transfer the mixture to a bowl, let it cool thoroughly, and then stir in 8 ounces of crumbled feta cheese.
Preheat the oven to 350 degrees Fahrenheit, and spay two baking sheets with cooking spray. Thaw 16 frozen phyllo sheets. Place 1 phyllo sheet on a work surface, with the short side nearest you, and brush the sheet with oil. Place a second sheet on top of the first, and brush it with oil as well. Cut the phyllo stack into four long strips. Spoon 1 1/2 tablespoons of the spinach-feta mixture onto the short end of the phyllo strip.
Fold the end of the strip over the filling to make a right triangle. Fold the pointed end toward the strip to seal the triangle. Continue folding the pointed ends up and over the phyllo strip to make a filled triangle. Repeat with the remaining filling and phyllo, brushing each phyllo sheet with oil. Bake the triangles until they are golden brown, about 15 to 20 minutes. Cool the triangles for at least 10 minutes before serving.