Wash the cucumbers thoroughly and slice them into rounds or half-moons, depending on your preference.
In a medium mixing bowl, combine the white vinegar, granulated sugar, salt, mustard seeds, celery seeds, turmeric powder, and red pepper flakes (if using). Whisk until the sugar and salt are dissolved.
Add the sliced cucumbers, garlic, and onion to the bowl. Mix everything together, ensuring the cucumbers are well coated with the brine.
Transfer the mixture into a glass jar or airtight container, packing the cucumbers tightly.
Pour any remaining brine over the cucumbers, ensuring they are fully submerged.
Seal the jar or container and place it in the refrigerator. Allow the pickles to marinate for at least 24 hours before enjoying for the best flavor.
Keep the pickles refrigerated and consume within 2-3 weeks for optimal freshness.