Combine the vinegar, water, sugar, and salt in a measuring cup and microwave until the sugar and salt dissolves (2-3 minutes).
Arrange the green onions, garlic, cilantro, mint, and red chili flakes in the bottom of a large bowl or container.
Layer the cucumber slices on top of the onions, garlic, and herbs.
Pour the brine over the cucumbers until they're fully submerged.
Cover the bowl and let the cucumbers rest in the refrigerator overnight.
These pickles will keep for several weeks in the fridge.