Remove the frozen phyllo sheet from the freezer and let it thaw in room temperature for about 2 hours. I used one roll from the package which had about 20 sheets.
I used frozen chopped spinach, so I thawed it in the microwave and then drained out all the liquid by squeezing the spinach. Keep this aside. If using fresh spinach, sauté it in a pan with a drop of oil for 3-5 minutes or until the spinach wilts and let out all the liquid and then drain out the liquid.
Grate the paneer and keep this aside as well.
In a pan, heat 1 tbsp of oil and add the cumin seeds. Let it splutter and then add the chopped onions. Sauté the onions until slightly brown. Now add the green chilies. Garam masala, salt, spinach and paneer and mix well. Cook this mixture on low flame for 2-3 minutes. Turn off the heat and keep aside.
Carefully unfold the phyllo sheet. Make sure that the sheets are completely thawed before unfolding or else it could crack and break in the middle.
Remove one sheet and place it carefully on the work surface. Using a pastry brush, brush some oil on the surface of the sheet and layer it with the second sheet. Repeat the same for 2 more times until you have 4 sheets stacked one on top of another.
Using a sharp knife or a pizza cutter, carefully cut the sheets into 4 strips (refer to the pictures).
Place a tablespoon of the spinach filling on each strip at one end of the sheet.
Fold the sheet over the filling forming a right angled triangle (refer to the picture). Now fold over again, maintain the triangle shape and repeat this until you reach the end. Brush the last piece of remaining dough with some oil and fold over and seal.
Repeat the same with the remaining sheets and place the prepared samosas in a greased baking sheet.
Preheat the oven to 375 F and then bake the samosas for 20-25 minutes. Rotate the tray once in between to ensure even baking.
Serve warm with any dipping sauce of your choice.