In a skillet heat oil, add onions and garlic and sauté over medium heat for a few minutes or until onion becomes translucent
Add spinach and cook a few minutes more until all the moisture has evaporated.
Lightly beat the egg in a medium-sized bowl. Add feta cheese, Vegetable Cubes and spinach mixture, stir until combined.
Remove phyllo sheets from package and place on a damp kitchen towel. Take top two sheets and place them on a clean cutting board or other work surface. Immediately place another damp kitchen towel on top of remaining phyllo sheets to keep them from drying out. Brush the two phyllo sheets (still stacked together) lightly with butte
Cut into four pieces (lengthwise then crosswise).
Place a heaping tablespoon of filling in one corner and fold it diagonally. Keep folding until you reach the end of the strip; tuck end in. Place triangles on ungreased cookie sheet. Continue doing this until all the phyllo sheets and filling until gone
Brush the tops of the triangles lightly with any remaining butter.
Bake in a single layer at 375°F (190°C) until golden brown (about 15 minutes). Alternatively you can freeze them and bake right from frozen (just add few minutes to baking time).