In a large mixing bowl combine the flour, baking powder, salt, caraway seeds, and onion. Mix well.
Add the olive oil and mix with a fork or hands until evenly mixed - there should be small crumbs.
Add the water and combine. The dough will look wet. Rest the dough at room temperature for 30 minutes; at this point, the dough will look much drier as the rye hydrates.
Cut the dough in half, one for each baking sheet. Roll the dough out on silicone baking sheets the size of a half-sheet pan. Roll out to the edges to cover the sheet completely. Once done, cut the short dimension in 4 slices, and the long dimension in 8. This will give 32 crackers per sheet. Either a pizza cutter or a steel, 18 inch ruler works well for this.
Alternately, roll dough in small pieces through a pasta roller. (About setting #2 on a Kitchenaid pasta attachment works well). Use a pizza cutter to trim to size - 3 strips will fit perpendicular to the long access of a half-sheet. Trimming each strip into 12 crackers gives a good size.
Bake for 12 to 14 minutes, switching the trays halfway through. Watch closely to bake to your desired doneness and toastedness. Cool for 10 minutes. Serve or store in an airtight container for up to 2 weeks.