Add flours, seeds, nutritional yeast, and spices to the bowl of a stand mixer fitted with a dough hook and stir until everything is well combined. (If you don't have a stand mixer, just work the dough using your hands.)
With the mixer running on low speed, slowly pour in the starter and olive oil and run for 2-3 minutes, or until the dough begins to form into a ball.
Remove the bowl from the stand mixer and finish mixing using your hands to make sure everything is evenly incorporated. Separate dough in half.
Roughly shape each half into a 1/2 inch thick rectangle, wrap in plastic or beeswax wrap and place in the fridge for at least 30 minutes.
Before beginning to shape the dough, preheat oven to 325°F.
Working with one at a time, remove dough from fridge and place onto a well-floured strip of parchment paper, about the size of your baking sheet. Evenly roll the dough out very thin, about 1/16 inch thickness. (If it's too thick, the crackers won't become crispy. The thinner the dough, the crispier the cracker.)
Brush the top of the dough with olive oil and sprinkle with flaky salt.
Using a pizza cutter, cut the dough in diagonal lines (about an inch apart) each way to form the cracker shapes. (Don't attempt to separate the crackers yet. That will be done after they bake.) Then, using a fork, poke holes in the center each cracker.
Transition dough and parchment paper onto a baking sheet and repeat the process with the second half of dough.
Place both baking trays in preheated oven and bake for 20-25 minutes total, rotating the trays about half way through so they bake evenly. Be sure to check at the 20 minute mark to avoid overcooking. The crackers should be starting to brown at the edges and a nice golden brown throughout.
Remove from the oven and allow the crackers to cool and continue to crisp up for another 10-15 minutes before separating and serving.