Make the semolina pudding. Bring water to a boil and add 4 really full tablespoons semolina flower whisking continuously as it cooks and thickens to avoid lumps. Cook for about 7-10 minutes whisking often as it might stick to the bottom of the pan, then set aside to cool.
In a large enough bawl, mix the fish roe for a couple of minutes then start adding the oil carefully, little by little. The fish roe will start to change color and lighten up. It will also increase in volume as it absorbs the oil. Continue adding 3/4 of the oil, then start alternating the oil with drops of lemon juice for acidity and sparkling water for fluffiness.Continue with the rest of the oil, taste and adjust the acidity. Start adding bits of semolina pudding and incorporate them mixing well. It's not necessary to add all the pudding, just add in batches and taste. We do not want to dilute the specific fish taste too much.
When everything tastes perfectly for you, add the very finely chopped onion and incorporate it well. Transfer to a serving bawl and decorate with olives, cucumber slices, radishes and fresh dill as it pairs perfectly here. Spread on crusty bread slices and enjoy!