In a medium bowl, stir together the chickpea flour, nutritional yeast, sugar, and salt. Add the oil, mustard and 4 tablespoons water, stirring until blended. The dough will seem dry at first, but keep stirring until completely blended. Add a bit more water, only if needed to combine all the dry ingredients. The dough should be smooth and stiff, but not sticky (see photos).

Divide dough in half. Shape one half into a a rough rectangle or square and place onto a large piece of parchment paper (about the size of the baking sheet) that has been lightly dusted with chickpea flour. Using a rolling pin, roll dough very thin into about a 12-inch by 8-inch rectangle. Tear off pieces of the dough and squish them into place, as much as needed, to make a relatively even rectangle.

Using a pizza cutter or large knife, cut the rectangle into 40 crackers. If desired, brush off any excess flour with a damp pastry brush and (optional) sprinkle with salt.