Peel and coarsely chop onions. Heath the olive oil in a skillet and saute the onions until slightly golden. Add the parsley, chives and basil, saute a few minutes more, stirring often.
Beat the eggs lightly with salt and pepper.
Stir the onions and herbs one more time, then distribute evenly in the skillet. Lower the heat as much as possible and cook until the eggs are barely firm on top, 10-15 minutes on very low heat.
Turn a large plate upside down over the skillet like a lid and overturn the skillet quickly, dropping the frittata onto the plate. Slide the frittata back into the skillet and brown the other side for a few minutes.
Turn the frittata onto a serving plate and cut into wedges just before serving. It may be eaten hot, cool or at room temperature.