In a deep bowl mix the eggs, yogurt, baking powder, pinch of salt and 3-4 tbsp oil, beat well.
Put 2-3 tbsp of the mixture onto a phyllo pastry sheet and spread it all over it using the spoon, then take a little feta cheese and crumble it along the entire sheet on top.
Grab 2 sheets (with filling on only 1 of them) and roll them up. Arrange the rolled up sheets in an oiled tray.
Repeat until you're out of sheets; you need to have a little of the egg and yoghurt mixture left (enough to smear 1 sheet).
To the remaining mixture add the carbonated water, stir carefully and pour it evenly over the arranged sheets.
Bake at 329°F (165 °C) for 10-15 min., then turn the heat up to 410°F (210 °C) until ready.