Pour the flour on your worktop and make a well in the middle. Mix in the olive oil, salt and sugar. Dissolve the fresh yeast in the water and pour the yeast mixture into the flour.
Knead the mixture by hand to obtain a homogeneous and smooth dough. Roll the dough into a ball, cover with a clean kitchen towel and let rise for at least 90 minutes in a warm place or overnight in the refrigerator, under cling film.
Just before baking, roll out the dough and flatten it to the desired thickness with the fingertips. Start in the middle and work towards the edges while you turn the pizza around.
Cover the pizza with the tomato base for pizza, chopped onions, tuna and mozzarella and bake in the oven. How long a pizza has to bake depends on the heat of your oven. But it's easy to see when your pizza is ready; it’s when the crust begins to brown and the ingredients melt. Keep an eye on your pizza regularly.