Combine all the dry ingredients (flour, oats, seeds, salt and herbs) in a bowl and mix with a spoon.
Pour the olive oil and the water into the bowl and knead all together until a dough is formed
Divide the dough in three pieces of the same size. Add the parmisan and the walnuts to the first piece of dough, the dried tomatoes to the second one, and the olives to the third one. Knead again all the three doughs until the ingredients are well incorporated.
Roll the dough with a rolling pin to a thin sheet, no thicker than about 2mm.
You can now create your crackers by cutting the dough with a knife or a pastry cutter (you can make them as big or small as you like)
Put your crackers on a baking tray covered with some parchment paper, and cook them in the oven at 180° for approximately 15-20 minutes (the cooking time depends on the size)
Your crackers are ready! You can store them in a airtight container for several weeks.