Soak the bread in water. In the meantime, in a food processor start mixing the fish roe and onion.
Squeeze all the water out of the bread and add to food processor, blend well, until there are no chunks of anything.
Add the breadcrumbs and dill and blend until smooth.
Add the lemon slowly while the food processor or blender is running.
Add the oil very-very slowly. Almost drop by drop, you want the oil to be completely absorbed as you are adding it. You will use about ½ cup.
Store in the refrigerator and let the flavors set in.
Serve with bread or bread sticks and olives and white wine.