Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with parchment paper. Cut a small square out of a separate sheet of parchment paper and oil 1 side; set aside.

Blend brown rice, quinoa, and tamari in a food processor, adding water if mixture is too dry, until a dough starts to form. Add chia seeds, sesame seeds, flax seeds, and salt; pulse until dough is a sticky ball.

Roll small pieces of dough into 1/2-inch balls and arrange at least 2 1/2 inches apart on the prepared baking sheet. Place the oiled square of parchment paper, oil-side down, onto a dough ball. Flatten the dough ball into a very thin 2-inch-wide disk by pressing the top of a small jar onto the parchment square. Repeat with remaining dough balls.

Bake in the preheated oven until edges of crackers begin to brown, 10 to 12 minutes. Transfer crackers to a wire rack. Place the rack onto the baking sheet and return to oven.

Bake until crackers are dry and crisp, 2 to 3 minutes more.