Preheat oven to 375°F.

Line a baking sheet with parchment paper.

In a medium bowl, combine oats, pumpkin seeds, sunflower seeds, sesame seeds, poppy seeds and salt. Add oil and water and stir to combine. Let stand 15 minutes, until mixture has absorbed moisture.

Stir oat mixture again then transfer to prepared baking sheet. Press second sheet of parchment over mixture and use your hands to press and pull it into a fairly even layer. Finish this process with a rolling pin, using it to flatten the cracker to an even layer 1/8" to 1/4"-thick. Remove and reserve top layer of parchment.

Bake cracker until edges are golden brown, about 15 minutes. Remove from oven and, using the parchment paper, carefully turn cracker over onto baking sheet (take care not to burn your hands!). Return to oven and bake until center is firm and golden brown around the edges, about 20 minutes. Let cool on baking sheet, then break with your hands into pieces of varying size. (Reserve any crumbles for use as salad toppings or even to top your morning yogurt.)