Combine poolish ingredients together in a bowl and stir until homogeneous. The bowl used need to have enough capacity for the mixture to double up in size. Cover with cling film and leave to ferment at room temperature overnight (8-10 hours).
Poolish focaccia dough
Combine the flour, water, 14 g of fine salt and all of the mature poolish and stir until homogeneous. Cover with cling film and let sit for 20 minutes (autolyse).
After 20 minutes, mix the dough with an electric mixer fitted with hook attachments for 5 minutes at low speed, then another 5 minutes at medium speed.
Wet your hand and slide it under the dough, catch it from below and lift one side upwards gently stretching it, then fold it over. Turn the bowl 90° and repeat: slide hand below, stretch upwards, fold over. Turn the bowl another 90° and repeat until you have stretched and folded the dough from all 4 cardinal points.
Repeat stretch and dough procedure 4 times, every 30 minutes, during the first 2 hours. Keep the dough in the bowl, covered with cling film in between stretch and fold sets.
Spread some olive oil onto a baking tin, then press down a baking paper sheet. Spread more oil over the baking paper, distributing it all over the surface.
After the last stretch and fold set, transfer the dough tot he baking tin, gently pulling it to fit the new container. Aprinkle some more oil over the focaccia surface, cover with cling film and let rest for 4 hours at room temperature.
Topping
Halve the cherry tomatoes and add them to a bowl. Add dried oregano, salt and olive oil and toss.
Coat your hand with more olive oil and proceed to press your fingers into the dough to create the typical focaccia pattern. This redistributes the pockets of air inside the dough.
Press the cherry tomatoes onto the focaccia dough, cut facing up. Sprinkle some salt flakes all over the focaccia surface.
Bake the focaccia in the preheated oven at 230°C (450°F) for 20-25 minutes.
If you have fresh oregano available, you can add some to the focaccia as garnish. Please notice that the leaves go brown if placed on hot focaccia, so reserve this decoration only if serving the focaccia cooled.