Mix the flour, baking soda and salt in a bowl. Then add the olive oil and tepid water, and continue mixing with a wooden spatula.
Knead with floured hands for about ten minutes. If necessary, add a little water or flour, so that the dough is not too sticky and holds well.
Form a ball and cover it with a damp cloth and let it rest for 30 minutes.
In the meantime, prepare the filling (see below).
Divide the dough into 6 balls of equal weight. Sprinkle your worktop with corn starch (or flour), and roll out the balls with a roller to form round patties about 22 cm in diameter, 3/4 mm thick.
Cook the piadina in a slightly oiled hot pan (or crepe pan) over medium heat. Count about 2 mn 30 / 3 mn per side, and crush the bubbles that form with a fork.