Thinly slice the onions and cucumbers and spread them out evenly in a single layer on a sheet pan.

Sprinkle the sea salt over the onion and cucumber slices and set aside to rest for 30 minutes.

Meanwhile, place the sour cream, white vinegar, allulose, dried dill, and dried parsley in a medium bowl and whisk until combined. Cover and refrigerate.

Blot the cucumber and onion slices with paper towel to soak up the liquid and then squeeze them by hand to release more moisture. Place them in a colander over the sink or a bowl and let drain for 30 minutes.

Once drained, remove the dressing from the fridge and gently toss in the dressing until coated.

Cover and refrigerate for at least an hour before serving.