Preheat the oven 200ºC.
Shred the spinach and chop the onion. Chop the garlic clove as well and set aside.
In a pan, on medium heat, heat the oil and saute the onion and garlic till they turn slightly golden-brown(about one minute).
Add the spinach and cumin to the pan. Cook until the water from the spinach evaporates. Keep stirring the spinach so it doesn't burn. This should roughly take about 7 - 8 minutes.
Once done, remove from heat and let it cool.
Add the feta cheese to this spinach mixture and mix thoroughly.
Cut long strips of the filo pastry - about 2 inches wide. Brush one pastry sheet with olive oil and place another sheet on top of it. The oil will make them stick together.
Place about 1-1/2 tablespoons of the spinach-feta mixture on one end of the sheet and keep folding it into triangles till the end. Seal the end with olive oil.
Repeat steps 7 and 8 till all the mixture is used.
Lightly oil a baking tray. Brush olive oil onto each Spanakopita parcel and place on the tray.
Bake for about 10 minutes - or until they turn golden brown.
Serve with Tzatziki sauce.