For the dough, combine the yeast and the tepid water. Set aside for 10 mins. The yeast will start to activate as a foam appears on the surface.
Add the water and yeast mix to the flour in a mixer with a dough hook attachment.
Add a pinch of salt and 1 tbsp olive oil. Turn on mixer, allowing to mix for 10 mins.
If you don’t have a mixer, combine all the ingredients in a bowl and mix by hand. Once the dough comes together move to a work surface and knead by hand for 10 mins, dust the work surface with a little flour to stop sticking, as this is a wetter dough. This kneading process is very important to activate the gluten in the flour that will result in a springy chewy texture in the final baked bread.
Place the dough in a large, lightly oiled bowl and cover with plastic wrap. Leave in a cool place to prove overnight. The dough will double in size and develop a nice fermented aroma.
In a small bowl combine onion chunks and rosemary and lightly dress with some olive oil. This will stop them from drying out when the bread bakes and helps the flavour transfer to the baking bread.
Take a deep sided baking tray (approximately 24cm x 34cm) and coat with a thin layer of olive oil using some paper towel. This will prevent the dough from sticking.
Scoop the dough from the bowl into the tray and stretch it gently to the edges.
Take 1/2 cup olive oil and pour it over the surface of the dough. Using the tips of your fingers push down to the tray base all over the surface of the dough.
Top the bread by pushing the chunks of onion and tomato into the bread to the base. The bread will bake around these but they will also stick out of the surface.
Take a damp tea towel and cover the tray and leave it to prove at room temperature for a further one hour.
Once proved sprinkle the bread with some flakey salt and bake at 220°C for 25 minutes or until golden brown.
Remove from the oven and allow the bread to cool before removing it from the tray.
Slice and enjoy.