Stir together flour, baking powder, and salt in a medium bowl. Add very coarsely freshly ground black pepper to taste and stir dry ingredients to incorporate. Make a well in centre, then add water and oil and gradually stir into the flour with a wooden spoon until a dough forms.
Knead dough gently on a work surface 4 or 5 times into a smooth ball. Divide dough into 6 equal pieces and roll out each of the dough pieces with a rolling pin on a lightly floured work surface, into a rustic long baton shape. The rolled dough should be very thin. Lightly brush the top of the flatbread with additional olive oil and sprinkle with sea salt and a little more pepper. (Roll out dough on a piece of parchment paper and transfer the whole sheet of parchment paper with the cracker dough on top to the cookie sheet, or just spray baking tray with cooking spray and bake directly on baking sheet.)
Bake the remaining dough in batches, until flatbread crackers are pale golden brown, 8 to 10 min. Let the baked crackers cool on wire racks. Flatbread crackers can be made 2 days ahead and cooled completely, then kept in an airtight container at room temperature.
Cook’s Note: Substitute pepper for other flavouring. You might try fresh herbs like rosemary, or thyme, or some parmesan cheese, or try adding nuts or seeds. Use your imagination and enjoy!