Mix sourdough starter, water, oil, sifted flour, and kosher salt together in the bowl of a mixer with a dough hook. Add a tablespoon of water at a time, if needed, for dough to come together. Rest for 10 minutes.
Next, knead the dough on low speed for about 4 minutes. Transfer to a large bowl coated with cooking spray and let rise for 4 hours, covered lightly with kitchen towel.
Turn dough onto floured surface, fold the dough over on itself 2-3 times, knead a couple of times, flatten and cut into 12 equal pieces.
Shape the dough into a ball and pat together to make a bagel shaped disc shape. Use your thumb to poke a hole through the middle of the dough, stretching to make the center hole. Place the shaped bagels on a parchment or silicone lined baking sheet. Cover the shaped bagels with a damp kitchen towel and let sit for about 1 hour to rise.
In a bowl mix together the sesame and poppy seeds, dried onion and garlic flakes, shredded Parmesan cheese and sea salt flakes or kosher salt (optional).
Preheat your oven to 450°F. Fill a large 12-inch skillet or wide stock pot half full with water and add the tablespoon of baking soda. Bring it to a boil. When the water is boiling, drop as many bagels as will fit, one at a time, into the boiling water. Boil for 1 minute total, turning at the 30 second mark. Use a slotted spoon to place the bagels back on the baking sheet. Continue until all the bagels have been boiled.
Brush the bagels with the egg wash and dip one side into everything seed mixture. Arrange seed side up on baking sheet. Bake for 14 minutes. Cool on a rack. Store in an airtight container.
If you are unsure of the natural yeast in your sourdough starter you can add 1 tbsp yeast and 3 tbsp sugar to the warm water initially in Step 1 above. Allow yeast to activate and bubble. After 5 minutes add to mix and continue with the directions as written.